End use applications of biodegradable polymers

ABSTRACT

Disclosed are products made of degradable materials which include a hydrolytically degradable polymer. The degradable materials can be internally or externally modified. The internally modified polymer composition has polymers modified by the use of comonomers having a relatively high molecular weight. The externally modified polymer composition includes a modifier, wherein the modifier is compatible with the polymer and the modifier is nontoxic, nonvolatile and nonfugitive. The various degradable materials include films, fibers, extruded and molded products, laminates, foams, powders, nonwovens, adhesives and coatings. The disclosed materials are particularly useful for the production of a variety of products in high volumes which are suitable for recycling after use or which are discarded into the environment in large volumes.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.08/128,520, filed Sep. 29, 1993, entitled "END USE APPLICATIONS OFBIODEGRADABLE POLYMERS", now U.S. Pat. No. 5,444,113, which is acontinuation-in-part of U.S. patent application Ser. No. 07/950,854,filed Sep. 22, 1992, entitled "Degradable Polymer Composition"; which isa continuation-in-part of Ser. No. 07/579,000, issued U.S. Pat. No.5,216,050, issued Jun. 1, 1993, entitled "Blends of Polylactic Acid";and Ser. No. 07/579,005, filed Sep. 6, 1990, U.S. Pat. No. 5,180,765,issued Jan. 19, 1993, entitled "Biodegradable Packaging Thermoplasticsfrom Polylactic Acid"; and of pending U.S. patent application Ser. Nos.07/579,460, entitled "Degradable Impact Modified Polylactic Acid"; andSer. No. 07/579,465, entitled "Biodegradable Replacement of CrystalPolystyrene"; all filed on Sep. 6, 1990; which are continuation-in-partsof U.S. patent application Ser. Nos. 07/387,676; 07/387,678; 07/386,844;and 07/387,670; respectively, all filed on Jul. 31, 1989, and nowabandoned; which are continuations-in-part of U.S. patent applicationSer. Nos. 07/229,894, filed Aug. 8, 1988; 07/229,896, filed Aug. 8,1988; 07/317,391, filed Mar. 1, 1989; and 07/229,939, filed. Aug. 8,1988; respectively, now abandoned; and all of which are incorporated byreference herein in their entirety.

FIELD OF THE INVENTION

The invention relates to degradable polymer compositions and processesfor forming various degradable materials including those compositions.The compositions and processes are useful for the production of avariety of products.

BACKGROUND OF THE INVENTION

Some polymers are known to degrade by hydrolysis in the presence ofwater and thereby decompose to smaller chemical units. Some of thesepolymers are also biodegradable, such as polylactic acid andpolyglycolic acid. Polymers such as polylactic acid and polyglycolicacid can be referred to generally as polydioxanediones because each isprepared by polymerization of a dioxanedione-based monomer. As usedherein, except as specifically noted otherwise, dioxaneone refers tocompounds having a dioxane ring with at least one carbonyl oxygenpendant from the dioxane ring. The remaining three carbon atoms in thedioxane ring may have various constituents pendant therefrom. Althoughthe term dioxaneone, which is also sometimes written as dioxanone, isoften used in a specific sense to refer to 2-keto-1,4-dioxane,dioxaneone is used herein in a general sense as discussed below, unlessotherwise specifically indicated by the general formula: ##STR1## whereR₁, R₂, R₃ and R₄ can be any of a variety of constituents and where Zcan be one or more constituents covalently bonded to the associatedcarbon atom in the dioxane ring. When all of R₁, R₂, R₃ and R₄ arehydrogen and Z is two hydrogen constituents, then the compound is2-keto-1,4-dioxane.

Dioxaneones such as lactide and glycolide, in which Z is a carbonyloxygen, may be more specifically referred to as dioxanediones since theyeach have two carbonyl oxygens pendant from the dioxane ring.Dioxanediones are cyclic diesters that may be represented by the generalformula: ##STR2## Where R₁, R₂, R₃ and R₄ can be any of a variety ofconstituents. When R₁, R₂, R₃, and R₄ are all hydrogen, then thecompound is glycolide which is also referred to as1,4-dioxane-2,5-dione. Although the term dioxanedione is sometimes usedto refer specifically to glycolide, the term as used herein is alwaysemployed in the general sense to indicate a class of compounds asindicated by the generic formula above, except as otherwise notedherein. When R₁ and R₃ are methyl and R₂ and R₄ are hydrogen thecompound is lactide, which may be also referred to as3,6-dimethyl-1,4-dioxane-2,5-dione. A polydioxaneone having one or morerepeating units representative of a dioxanedione monomer may be morespecifically referred to as a polydioxanedione. When a dioxaneonecontains one or more asymmetrical carbon atoms, such as is the case withlactide, then that particular dioxaneone can exist as various opticalisomers. For example, lactide can exist as two optically active isomers,D-lactide and L-lactide, or as the optically inactive isomermeso-lactide. D-lactide and L-lactide can also be present in equalquantities to form an optically inactive mixture known asracemic-lactide. Both meso-lactide and racemic-lactide are oftendesignated as simply D,L-lactide.

Higher molecular weight polymers can be produced by ring-openingpolymerization of dioxanedione monomers. Dioxanediones used as monomersto produce higher molecular weight polymers have traditionally been madefrom low molecular weight poly-α-hydroxycarboxylic acids by adepolymerization reaction often referred to as "backbiting." Thebackbiting process is relatively expensive, contributing to the lack offeasibility in developing low-cost consumer products for mass-marketapplications using polydioxanedione polymers.

Due to the expense and difficulty in preparing hydrolytically degradablepolymers such as polydioxanedione, their use has been largely confinedto high value medical applications where bioabsorbable materials arerequired. Most reported medical applications involve internal use of thepolymers, such as for sutures, prosthetic devices, and drug releasematrices. Some polymers that have received considerable attention formedical applications include polylactic acid, polyglycolic acid,poly-ε-caprolactone and polydioxanone.

Some attempts have been made in the medical field to vary properties ofbioabsorbable polymers based on the specific intended use. Propertiesthat have received some attention include strength, flexibility, andrate of hydrolytic degradation. It is generally known that a copolymerusually exhibits different properties from homopolymers of eitherindividual comonomer. Some attempts have been made to develop specificcopolymers for specific medical applications.

Many references, however, identify several possible comonomers withoutany consideration for the possible effects that such comonomers mighthave on properties of the copolymer. For example, U.S. Pat. No.2,703,316 by Schneider, issued Mar. 1, 1955, discusses lactide polymersand copolymers capable of being formed into a tough, orientable,self-supporting thin film with up to 50% of another polymerizable cyclicester having a 6- to 8-membered ring. The patent specifically disclosespolymerization of 5 parts lactide and 5 parts glycolide and alsopolymerization of 12 parts lactide and 2 parts tetramethylglycolide, butalso provides an extensive list of other possible comonomers with noelaboration on polymer properties.

A few references have suggested the use of hydrolytically degradablepolymers outside of the medical field. For example, U.S. Pat. No.4,057,537 by Sinclair, issued Nov. 8, 1977, discusses copolymers ofL-lactide and ε-caprolactone prepared from a mixture of comonomerscontaining from about 50 to about 97 weight percent L-lactide and theremainder ε-caprolactone. Strength and elasticity are shown to varydepending on the relative amounts of L-lactide and ε-caprolactonemonomers. Depending upon the L-lactide/ε-caprolactone ratio, thepolymers are disclosed to be useful for the manufacture of films,fibers, moldings, and laminates. However, no specific applications arediscussed. Sinclair discloses that plasticizers may be added to thecopolymer if desired, but provides no guidance concerning what compoundsmight be suitable. Lipinsky et al., 1986, pp. 26-32, "Is Lactic Acid aCommodity Chemical," Chemical Engineering Process, August, discloses theuse of polylactic acid for packaging material without discussingmodifications of material properties by inclusion of plasticizers orother components.

Although it has been noted that suitable compounds, such asplasticizers, may be added to modify the properties of somehydrolytically degradable polymers, such as in U.S. Pat. No. 4,057,537just discussed, little guidance has been given as to what compoundsmight be effective. Identifying suitable compounds for use in externallymodifying and identifying suitable comonomers for internally modifyingthe properties of biodegradable polymers has been a major problemconfronted in developing biodegradable polymers for mass-marketedproducts. Relatively few references discuss modification of propertiesof hydrolytically degradable polymers with external compounds, such aspolylactide homopolymers and copolymers. The medical industry hasgenerally sought to tailor polymer compositions to specific medicalapplications by developing specific copolymers, rather than to addexternal compounds. Those references that do discuss compounds, such asplasticizers, however, offer little guidance in selecting suitablecompounds to be used for mass-marketed, hydrolytically degradablepolymer products.

Compounds which effectively modify properties of polymer products arenot to be confused with compounds that are designed only to aid polymerprocessing and that are removed prior to or during manufacture of thefinal product. Compounds which are effective in modifying properties ofpolymer products should be completely miscible with the polymer,nonvolatile, and should not migrate to the surface of the polymercomposition, as might be desirable with a processing aid.

Plasticizers or other similar compounds used in mass-marketed productsmade of hydrolytically degradable polymers will be deposited into theenvironment in large quantities upon degradation of the polymers.Therefore even low levels of toxicity are a concern due to thepotentially huge quantity of potential waste.

Thus, a need exists for degradable polymer compositions that aresuitable for use with products that can replace existing non-degradableproducts that are rapidly becoming difficult to dispose of due tolimited landfill space and other environmental concerns.

SUMMARY OF THE INVENTION

The present invention is directed toward a variety of products which aremade of degradable materials. The degradable materials include ahydrolytically degradable polymer, such as polylactic acid. Thehydrolytically degradable polymer can either be an externally or aninternally modified polymer. The internally modified polymer is modifiedby the inclusion of other comonomers in the polymer molecule asdescribed in more detail below. The externally modified polymercomposition includes a modifier that is compatible with the polymer andis nontoxic, nonvolatile and nonfugitive. The polymer and modifier arecompatible with each other and typically have solubility parameterswhich are within about 1.0 (calorie per cubic centimeter)⁰.5 of eachother and the solubility parameters are typically between about 7.5 andabout 16.5 (calories per cubic centimeter)⁰.5. The modifier isnonvolatile and typically has a vapor pressure of less than about 50Torr at 180° C. and a boiling temperature above about 280° C. at 1atmosphere.

The degradable materials of the present invention are useful for theproduction of commercial and consumer products. Such products include,for example, products for controlled release of chemicals, oral drugdelivery products, automobile products, gardening products, consumerproducts, health products, substrates that are suitable for theattachment and growth of living cells, construction products, adhesiveproducts, absorbent articles, flammable products, lubricants, bags,netting, rope, coatings, filters, inks, containers, packaging, clothing,and paper goods. The degradable materials of the present invention areparticularly useful for the production of frequently littered products,such as drink containers, labels, food packaging, printed matter,construction material and vehicle supplies.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed toward a variety of products which aremade of degradable materials. The degradable materials can includeeither or both of an externally or an internally modified polymercomposition, as those terms are described below.

DEGRADABILITY

As used herein, the term "degradable," with reference to the variousmaterials of the present invention refers to a material including adegradable polymer as described below and in the proportions describedbelow. The term "degradable," with reference to the polymer, refers to apolymer having a polymer molecular structure which can decompose tosmaller molecules. As discussed below, the degradable polymer can behydrolytically degradable in which water reacts with the polymer to formtwo or more molecules from the polymer.

The polymer of the present materials is further characterized as beingdegradable within a time frame in which products made from thematerials, after use, can either be readily recycled by decomposition ofthe polymer into its monomeric units or, if disposed of in theenvironment, such as in landfills, the polymer degrades quickly enoughto avoid significant accumulation of discarded products or wherein therate of accumulation is significantly less than that of similar productswhich are not degradable. The materials of this invention degrade in atime period of a few months to a few years, whereas similarmass-produced, nondegradable products require, typically, decades tocenturies.

The degradation characteristics of the polymer in the present materialsdepend in large part on the type of material being made with thepolymer. Thus, the polymer needs to have suitable degradationcharacteristics so that when processed and produced into a finalmaterial, the material does not undergo significant degradation untilafter the useful life of the material. Therefore, different embodimentsof the present invention will have different degradationcharacteristics. The timing of degradation of the materials can beevaluated by accelerated short-term testing under which materials areexposed to harsh conditions. For example, a useful test for degradationis an accelerated short-term test in which materials are subjected to atemperature of 95° F. (35° C.) and 95% humidity. Under these conditions,in a preferred embodiment, a test sample of material which is in theconfiguration of a 1-3 mil film is considered to be degradable if itbecomes sticky to the touch, cloudy, opaque or embrittled typically inless than about three months. Under these same conditions, in apreferred embodiment, a test sample of material which is in theconfiguration of a 1-3 mil film is considered to be degradable if it hasa tensile strength loss or a molecular weight loss of at least about 90%in less than about six months.

The polymer of the present invention can also be used to producearticles which, because the articles require durability in the use forwhich the article is designed (e.g., tires and hospital supplies), arenot degradable under ambient conditions within the time frame of theuseful life of the article. As such, in another aspect of the presentinvention, the polymer can be used to produce such durable articles.Such articles are, nonetheless, considered to be degradable and areparticularly useful because they can be treated to acceleratedegradation and therefore are degradable upon demand. For example, thepolymer can be exposed to environmental conditions which acceleratedegredation as, for example, being treated with increased temperature,and/or increased pressure, and/or increased humidity, and/or exposed tosuitable catalysts.

The polymer of the present invention can be characterized as beinghydrolytically degradable. As used herein, the term "hydrolyticallydegradable" refers to a composition in which chemical bonds in themolecule are subject to hydrolysis, thus producing smaller molecules. Ina further embodiment of the present invention, the polymer isbiodegradable. Biodegradability refers to a compound which is subject toenzymatic decomposition, such as by microorganisms, or a compound,portions of which are subject to enzymatic decomposition, such as bymicroorganisms. In one instance, for example, a polymer such aspolylactic acid can be degraded by hydrolysis to individual lactic acidmolecules which are subject to enzymatic decomposition by a wide varietyof microorganisms. Microorganisms typically can consumehydroxycarboxylic acid-containing oligomers with molecular weights of upto about 1000 daltons, and preferably up to about 600 daltons, dependingon the chemical and physical characteristics of the oligomer.

EXTERNALLY MODIFIED POLYMER COMPOSITION

Polymers

The polymer of the present composition can be an externally modifiedpolymer and can be selected from a variety of nontoxic degradablepolymers. Typically, the polymer should have a weight average molecularweight of between about 5,000 and about 1,500,000. Appropriate molecularweights will vary according to desired material type and will bediscussed more fully below.

The polymer of the present composition can be a homopolymer, acopolymer, or a physical blend of homopolymers and/or copolymers.Typically, the polymer of the present materials includes repeatingmonomer or comonomer units which are selected from the following groupand which polymers are non-toxic and degradable: ##STR3## wherein X isthe same or different and is O or NR' with R' independently being H,hydrocarbyl, or substituted hydrocarbyl; R₁, R₂, R₃ and R₄ can be thesame or different and are hydrogen, hydrocarbyl containing 1 to 24carbon atoms, or substituted hydrocarbyl containing 1 to 24 carbonatoms, and where n₁ and n₂ can be the same or different and are aninteger of from 1-12.

The polymer of the present invention typically includes the aboverepeating monomer or comonomer units in an amount of at least about 5weight percent, more preferably at least about 10 weight percent andmore preferably at least about 20 weight percent. Preferably, thepolymer includes a high enough percentage of polymerized monomers whichare hydrolytically degradable so that, upon degradation, polymerfragments of less than about 600 molecular weight are produced becausesuch polymer fragments are small enough to be metabolized bymicroorganisms.

The nontoxic degradable polymer of the present materials can be moreparticularly characterized as having repeating monomer or comonomerunits selected from the group consisting of: ##STR4## wherein X is thesame or different and is O or NR' with R' independently being H,hydrocarbyl, or substituted hydrocarbyl; R₁ and R₂ can be the same ordifferent and are hydrogen, hydrocarbyl containing 1 to 24 carbon atoms,or substituted hydrocarbyl containing 1 to 24 carbon atoms, and where n₁and n₂ can be the same or different and are an integer of from 1-12.

The polymer of the present materials is more particularly characterizedas comprising repeating monomer or comonomer units derived from monomersselected from the group consisting of alpha-hydroxycarboxylic acids,beta-hydroxycarboxylic acids, gamma-hydroxycarboxylic acids,delta-hydroxycarboxylic acids, epsilon-hydroxycarboxylic acids,beta-lactones, gamma-lactones, delta-lactones, epsilon-lactones,beta-lactams, gamma-lactams, delta-lactams, epsilon-lactams, cyclicdiesters of alpha-hydroxycarboxylic acids, dioxanones, substitutedvariations of the foregoing compounds, and combinations thereof. Thepolymer of the present materials is further characterized as comprisingrepeating monomer or comonomer units derived from monomers selected fromthe group consisting of lactic acid, glycolic acid,epsilon-hydroxycaproic acid, lactide, glycolide, epsilon-caprolactone,delta-valerolactone, substituted variations of the foregoing compounds,and combinations thereof.

In a more preferred embodiment, the polymer comprises repeating monomeror comonomer units derived from lactic acid which can be the result ofdirect polymerization of lactic acid or the polymerization of lactide.Preferably, the polymer typically includes more than about 50 weightpercent repeating units derived from lactic acid or lactide, and morepreferably greater than about 75 weight percent. In another embodiment,the polymer is prepared from polymerization of a composition includinglactide in which greater than about 50% by weight of the lactide isoptically active and less than 50% is optically inactive lactideselected from the group consisting of racemic D,L-lactide andmeso-lactide.

In a more preferred embodiment of the invention the polymer ispolylactic acid and has the repeating units of the formula, ##STR5##wherein n is the number of repeating units and n is an integer equal toat least about 150 and preferably 150≦n≦20,000. Preferably theunoriented composition has the physical properties of: a tensilestrength of about 300 to about 20,000 psi, an elongation to failure ofabout 2 to about 1,000 percent, and a tangent modulus of about 1,000 toabout 500,000 psi.

Those skilled in the art will recognize that this wide latitude ofproperties must be accommodated to serve the varied needs of theplastics industry. A review of this range of properties is found incommonly assigned U.S. Pat. No. 5,180,765, issued Jun. 1, 1993, entitled"Biodegradable Packaging Thermoplastics From Polylactic Acid". Forexample, presently used commodity thermoplastics vary considerably byuse. Stiff thermoforms, such as are used in salad covers are typicallyserved by thermoplastics such as polystyrene, which will be oriented tohave a tensile strength of about 7500 psi, and elongation to break ofabout 4%, and an elastic modulus of about 350,000 psi. At the otherextreme, pliable films for trash bags use plastics with a tensilestrength of about 1500 psi, elongations of 500%, and an elastic modulusof about 25,000 psi.

External Modifiers

The modifier for the externally modified polymer composition of thepresent materials is a compound which introduces pliability, flexibilityand toughness into a polymer composition to an extent that may not befound in the polymer-only composition. Also, addition of modifiers tothe polymer composition can reduce the melt viscosity of the polymer andlowers the temperature, pressure, and shear rate required to melt formthe polymer. Further, the modifier can add impact resistance to thepolymer which is not found in the polymer-only composition. Thus, themodifier of the present materials can be considered as a compatibilizer,flexibilizer or plasticizer.

The modifier is also considered to lower the glass transitiontemperature (T_(g)) of a polymer. Typically, the modifier of the presentmaterials will modify the T_(g) of the various materials to varyingdegrees, depending upon the intended end use of the material. Indiscussion of various specific embodiments of materials of the presentinvention, which are discussed below, various T_(g) parameters areprovided.

A further aspect of the present materials is that the modifier componentis nonvolatile. Thus, an important characteristic of the presentmaterials is that during polymerization and processing of the materials,the modifier does not volatilize so that subsequent to polymerizationand processing of the polymer composition into materials, the modifiersubstantially remains in the materials. Typically, a nonvolatilemodifier refers to a modifier in a polymer/modifier material in whichless than about 25 weight percent of the modifier initially presenteither before polymerization or before processing is lost due tovolatilization of the modifier during the production of the material,more preferably less than about 5 weight percent, and even morepreferably less than about 1 weight percent. Such modifiers aretypically compounds which have a vapor pressure of less than about 50Torr at 180° C., more preferably less than about 10 Torr at 180° C., andeven more preferably less than about 1 Torr at 180° C. Such modifierstypically have a boiling point above about 280° C. at atmosphericpressure, more preferably above about 340° C., and even more preferablyabove about 400° C.

A further aspect of the nonvolatility of the modifier is that themodifier can be nonvolatile due to strong polar characteristics of themodifier. Such polar characteristics are illustrated by those of thediscussion below regarding the role of polar characteristics incompatibility of the polymer and modifier.

Those skilled in the art will recognize the difference between amelt-processing aid and a modifier, such as a plasticizer. Amelt-processing aid permits easier processing, i.e., lower processingtemperatures and viscosities of the polymer melt, while a modifierimparts an attenuation of certain end-use properties, e.g., modulus. Insome instances, it is preferable to have a volatile additive for use asa melt processing aid so that processing is facilitated, and followingprocessing, the additive can be removed by volatilization to allow moredesirable strength or other physical property to develop. For example,lactide can be added as a processing aid to polylactide in a twin-screwcompounder that transports the melt blend to an extruder where thelactide is removed, either at a later zone or the die of the extruder.In this way, stiff polylactide compositions without a modifier can bemelt fabricated without sacrificing processability.

A further aspect of the materials of the present invention is that themodifier is nonfugitive. The term nonfugitive refers to a modifier thatdoes not escape from the material during the useful life of thematerials. That is, the modifier remains substantially intimatelydispersed in the polymer for the useful life of the material. Forexample, fugitive materials, which may initially be present as adiscrete phase, can become soluble in the polymer and migrate towardsthe surface of a material to form a surface film or vapor. That is,fugitive modifiers are not compatible with the polymer over time to anextent which impedes the intended function of the material. Typically,modifiers in a polymer/modifier material are considered nonfugitive whenless than about 30 weight percent of the modifier present in theprocessed material is lost due to becoming fugitive during the usefullife of the material, that is, during the time period from after thematerial is processed until the time the ultimate consumer discards thematerials, more preferably less than about 10 weight percent and morepreferably less than about 1 weight percent.

The modifier is preferably selected from the group consisting ofdicarboxylic acids, derivatives of dicarboxylic acids, polyesters ofdicarboxylic acids, tricarboxylic acids, derivatives of tricarboxylicacids, polyesters of tricarboxylic acids, cyclic diesters ofalpha-hydroxycarboxylic acids, derivatives of cyclic diesters ofalpha-hydroxycarboxylic acids, oligomers of cyclic diesters ofalpha-hydroxycarboxylic acids, beta-lactones, delta-lactones,gamma-lactones, ε-lactones, oligomers of alpha-hydroxycarboxylic acids,esters of oligomers of alpha-hydroxycarboxylic acids, benzoic acidderivatives, epoxy derivatives, glycol derivatives, phthalic acidderivatives, phosphoric acid derivatives, ketones, amides, nitriles, andcombinations of the foregoing.

The modifier is more preferably selected from the group consisting ofadipic acid derivatives, azelaic acid derivatives, cyclic esters ofoligomers of lactic acid, esters of oligomers of lactic acid, citricacid derivatives, polyesters of adipic acid, polyesters of azelaic acid,polyesters of sebacic acid, sebacic acid derivatives, benzoic acidderivatives, epoxy derivatives, glycol derivatives, phthalic acidderivatives, phosphoric acid derivatives, and combinations thereof.

The modifier is more preferably selected from the group consisting ofdi-n-hexyl adipate, bis(2-ethylhexyl)adipate, diisodecyl adipate,bis(2-butoxyethyl) adipate, bis(2-ethylhexyl)azelate, lactide,epsilon-caprolactone, glycolide, delta-valerolactone, oligomeric lacticacid, oligomeric lactic acid ethyl ester, acetylated lactoyllactateethyl ester, tri-n-butyl citrate, tri-n-butyl acetylcitrate, diethyleneglycol dibenzoate, dipropylene glycol dibenzoate, epoxidized soy oil,2-ethylhexyl epoxy tallate, diethylene glycol dinonanoate, triethyleneglycol di(2-ethylbutyrate), pentaerythritol esters, alkoxy sucrose andglucose, acylated sucrose and glucose, alkylated and acylated glycols,starch esters, N-acylated amino acid esters, amide derivatives andoligomers of N-acylated amino acid esters, polyethylene glycol esters,tri(2-ethylhexyl)phosphate, diemethyl phthalate, diethyl phthalate,butyl 2-ethylhexyl phthalate, bis(2-ethylhexyl)phthalate, dicyclohexylphthalate, diphenyl phthalate, adipic acid polyester with molecularweight from about 190 to about 6000, azelaic acid polyester withmolecular weight from about 232 to about 7500, sebacic acid polyesterwith molecular weight from about 246 to about 8000, di-n-butyl sebacate,and bis(2-ethylhexyl)sebacate, and combinations thereof.

The modifier is more preferably selected from the group consisting ofdi-n-hexyl adipate, bis(2-butoxyethyl)adipate, bis(2-ethylhexyl)azelate,lactide, epsilon-caprolactone, glycolide, delta-valerolactone,oligomeric lactic acid, oligomeric lactic acid ethyl ester, tri-n-butylcitrate, tri-n-butyl acetylcitrate, dipropylene glycol dibenzoate,epoxidized soy oil, 2-ethylhexyl epoxy tallate, diethylene glycoldinonanoate, triethylene glycol di(2-ethylbutyrate), butyl 2-ethylhexylphthalate, bis(2-ethylhexyl)phthalate, dicyclohexyl phthalate, adipicacid polyester with molecular weight from about 190 to about 6000,azelaic acid polyester with molecular weight from about 232 to about7500, sebacic acid polyester with molecular weight from about 246 toabout 8000, di-n-butyl sebacate, and combinations thereof.

The modifier is more preferably selected from the group consisting ofdicarboxylic acids, derivatives of dicarboxylic acids, polyesters ofdicarboxylic acids, tricarboxylic acids, derivatives of tricarboxylicacids, polyesters of tricarboxylic acids, cyclic diesters ofalpha-hydroxycarboxylic acids, derivatives of cyclic diesters ofalpha-hydroxycarboxylic acids, oligomers of cyclic diesters ofalpha-hydroxycarboxylic acids, beta-lactones, delta-lactones,gamma-lactones, ε-lactones, oligomers of alpha-hydroxycarboxylic acids,esters of oligomers of alpha-hydroxycarboxylic acids, and combinationsof the foregoing.

The modifier is further preferably selected from the group consisting ofadipic acid derivatives, azelaic acid derivatives, cyclic esters,oligomers of lactic acid, esters of oligomers of lactic acid, citricacid derivatives, polyesters of adipic acid, polyesters of azelaic acid,polyesters of sebacic acid, sebacic acid derivatives, and combinationsthereof.

The modifier is further preferably selected from the group consisting ofdi-n-hexyl adipate, lactide, epsilon-caprolactone, glycolide,delta-valerolactone, oligomeric lactic acid, oligomeric lactic acidethyl ester, tri-n-butyl acetylcitrate, adipic acid polyester withmolecular weight from about 190 to about 6000, azelaic acid polyesterwith molecular weight from about 232 to about 7500, and combinationsthereof.

In one aspect of the present invention, and particularly when thepolymer includes lactic acid-derived repeating units, preferredmodifiers include lactic acid, lactide, oligomers of lactic acid,oligomers of lactide and mixtures thereof. The preferred oligomers oflactic acid and oligomers of lactide are defined by the formula:##STR6## where m is an integer: 2≦m≦75. Preferably m is an integer:2≦m≦10.

Further modifiers useful in the invention include oligomeric derivativesof lactic acid and lactide selected from the group defined by theformula: ##STR7## where R=H, alkyl, aryl, alkylaryl or acetyl, and R issaturated, where R'=H, alkyl, aryl, alkylaryl or acyl, and R' issaturated, where R and R' cannot both be H, where q is an integer:2≦q≦75. Preferably, q is an integer: 2≦q≦10.

The modifier in the present materials is preferably in an amount greaterthan about 0.1 weight percent, more preferably greater than about 1weight percent, more preferably greater than about 5 weight percent, andmore preferably greater than about 10 weight percent. Also, the modifierin the present materials is preferably in an amount less than about 60weight percent, more preferably less than about 50 weight percent, andmore preferably less than about 40 weight percent. For purposes ofdisclosure herein, each of the above minimum values can be associatedwith each of the maximum values.

Compatibility

A further important characteristic of the present degradable materialsis that the modifier and degradable polymer are compatible. A compatiblemodifier generally refers to a modifier which is intimately dispersible,as that term is defined below, in the polymer and to a polymer which isswellable in the modifier. As used herein, where the modifier is aliquid at the mixing temperature, the term "swellable" means that thepolymer will expand in volume to at least about 120% of its initialvolume in the presence of excess modifier.

More particularly, the term "compatibility" refers to a modifier whichis thermally compatible with the polymer composition such that uponprocessing and use of the composition, the modifier and polymer remainas uniform mixtures, i.e., one that is not cheesy in appearance andwithout significant change in the relative proportions of thecomponents. Compatible mixtures typically are clear, non-oily, and thematerial does not stress craze easily. One useful indicator of thecompatibility of a modifier and polymer is the difference between thesolubility parameters of the polymer and modifier. The term "solubilityparameter" is also referred to as Hildebrand constant and is given inunits of energy per volume, such as calories per cubic centimeter(cal/cm³). Solubility parameters can be calculated by known methodsshown in the literature. A solubility parameter is a measure of theinternal attractive force that molecules of the same compound have foreach other. Thus, for two different compounds having similar solubilityparameters, the two compounds are likely to be readily as soluble withmolecules of the other compound as they are with molecules of the samecompound. It should be noted that while solubility parameters are usefulin assessing compatibility, they are not absolute predictors.Calculations of solubility parameters, for instance, do not account forall aspects of the chemical structure of a molecule. Thus, chemicalfeatures, such as polar character which is discussed below, and others,can make otherwise incompatible species compatible and vice versa.

Typically, the solubility parameters of the polymer and modifier arewithin about 1.0 cal/cm³, preferably within about 0.75 cal/cm³, and morepreferably within about 0.5 cal/cm³. The solubility parameters of themodifier and the polymer are also typically each in the range of fromabout 7.5 cal/cm³ to about 16.5 cal/cm³, more preferably between about8.0 cal/cm³ to about 12.6 cal/cm³ and more preferably between about 9.0cal/cm³ and about 11.0 cal/cm³.

A first parameter for determining compatibility is the difference insolubility parameters between the polymer and the modifier. It has beensurprisingly found, however, that polymer/modifier combinations whichhave solubility parameter differences outside of the parametersdiscussed above, can be compatible if the polymer and modifiers havesuitable polar characteristics which provide sufficient polar attractionbetween the species to make the polymer and modifier compatible. Forexample, it has been found that a polymer and modifier having solubilityparameters of about 9.57 and about 14.39, respectively, are compatible.In this instance, the polymer is a 90/10 L-lactide/D,L-lactide copolymerand the modifier is N-ethyl o,p-toluene sulfonamide. Relevant polarcharacteristics, include hydrogen bonding index, dielectric constant,and dipole moment.

One measure of polar interaction between two materials is the hydrogenbonding index. This index is derived from the infrared spectral shiftsof deuterated methanol when complexed with the substance underinvestigation. Preferably, the hydrogen bonding indices of the polymerand modifier are within less than about 10 units of each other, morepreferably, less than about 5 units of each other and more preferablyless than about 2 units of each other.

The dielectric constant of a substance refers to its ability to resistthe transmission of an electrostatic force from one charged body toanother. Preferably, the dielectric constants of the modifier andpolymer, at 25° C., are within about 20 units of each other, morepreferably within about 5 units of each other, and even more preferablywithin about 2 units of each other.

A further component of compatibility between the polymer and modifier isthe relative dipole moments of the polymer and modifier. The term"dipole moment" refers generally to the polarity of molecules and, moreparticularly, is the distance between charges multiplied by the quantityof charge in the electrostatic portions of the molecule. Typically, thedipole moments of the polymer and modifier are within about 6 units ofeach other, more preferably within about 2 units of each other, and evenmore preferably within about 1 unit of each other.

Another aspect of compatibility is the similarity between the polymerand modifier in terms of hydrophilic lipophilic balance ("HLB"). HLB isa measure of a material's relative hydrophilic and lipophilic nature.HLB has scale of zero to 20 in which a fully hydrophilic material wouldbe 20 and a saturated hydrocarbon would be zero. The HLB of compoundswith both hydrophilic and lipophilic portions is determined by dividingthe weight percent of the hydrophilic portion by 5.

The HLB value of polylactic acid is approximately 10 and that ofpolyglycolic acid is approximately 15. Lactide has an HLB of 12 andglycolide is 15. A typical good plasticizer for polylactic acid isdimethyl adipate (HLB=10). This plasticizer did not function withpolyglycolic acid. A plasticizer that functioned marginally withpolylactic acid was lauronitrile. It has an HLB of 3, but itshydrophilic group is extremely polar.

The HLB values of the plasticizer should be within about 4 units, andpreferably within 2 units, of the polymer to be plasticized. Specialcircumstances can stretch the range to about 7 HLB units.

It has also been found that when polymers of the present invention areable to adopt varied three-dimensional configurations, the polymers arecompatible with a wide variety of modifiers. For example, polymers whichare less crystalline in nature are typically able to adopt more variedthree-dimensional structures than polymers which are relativelycrystalline. Copolymers are usually less crystalline in nature thanhomopolymers. As a specific example, a copolymer with monomeric unitsselected from L-lactide, D-lactide and glycolide is typically lesscrystalline than homopolymers of any of the three materials.

Typically, polymers which have less than about 20 percent crystallinity,more preferably less than about 10 percent crystallinity, and morepreferably less than about 5 percent crystallinity have suitably variedthree-dimensional configurations for advantageous compatibilitycharacteristics. Crystallinity can be measured by various standardtechniques. In addition, as noted above, the polymers of the presentinvention are preferably copolymers, more preferably copolymers in whichno one monomer constitutes more than about 95 weight percent of thepolymer, more preferably no one monomer constitutes more than about 85weight percent of the polymer and more preferably no one monomerconstitutes more than about 75 weight of the polymer.

Nontoxicity

The reference to the polymer and modifier of the present material beingnon-toxic refers to the materials being non-toxic subsequent toprocessing, during use and subsequent to discard into the environment,including the degradation products of the polymer being nontoxic. Forexample, a material such as glycerin, which is on the FDA generallyregarded as safe (GRAS) list, can be used as a plasticizer, but undercertain processing conditions can be converted to acrolein, which is asuspected carcinogen. Thus, the various materials of the presentinvention can be processed so that otherwise non-toxic materials are notconverted to toxic materials.

As used herein, the term "nontoxic" generally refers to substanceswhich, upon ingestion, inhalation, or absorption through the skin by ahuman or animal, do not cause, either acutely or chronically, damage toliving tissue, impairment of the central nervous system, severe illnessor death. The term "nontoxic" can also refer to compounds, thehydrolysate or metabolites of which can be incorporated innocuously andwithout harm to the ecosystem. Preferably, the nontoxic polymer andmodifier of the present materials are generally regarded as safe (GRAS)as that term is used by the United States FDA, or any other similarclassification which may be used in the future. The toxicity level, asindicated by the Hazardous Substance Data Base of the National Libraryof Medicine, is an important factor in determining the suitability ofeach polymer and modifier for each application.

Preferred nontoxic modifiers include modifiers selected from the groupconsisting of acetyl tributyl citrate, lactide, glycolide, lactic acidesters, dimethyl adipate, diethyl adipate, caprolactone, acetyl triethylcitrate, bis 2-ethyl hexyl sebacate, bis 2-ethyl hexyl adipate, dibutylsebacate, and triethyl citrate. Even more preferred nontoxic modifiersof the present invention are selected from the group consisting ofacetyl tributyl citrate, lactide, glycolide, lactic acid esters,dimethyl adipate, diethyl adipate, caprolactone, acetyl triethylcitrate, bis 2-ethyl hexyl sebacate and bis 2-hexyl adipate.

INTERNALLY MODIFIED POLYMER COMPOSITIONS

Polydioxaneones and Nitrogen Analogues

Materials of the present invention, which involve internally modifiedpolymer compositions, comprise polymers, generally referred to herein aspolydioxaneones, having first repeating units of the formula ##STR8##where, independently for each such first repeating unit: X₁ and X₂ areindependently O or NR' and R' is independently H, hydrocarbyl,substituted hydrocarbyl or a hydrocarbyl derivative, includinghetero-atom containing constituents; R₁, R₂ and Z₁ combined have at mostone carbon atom; R₃, R₄ and Z₂ combined have at most one carbon atom;and Z₁ and Z₂ are each independently one or more constituent group(e.g., hydrogen, hydrocarbyl, oxygen, etc.) extending from the polymerbackbone chain and being covalently bonded to a tetravalent carbon atomin the polymer backbone chain, at least one of Z₁ and Z₂ being an oxygenthat forms a carbonyl group with the associated carbon atom in thepolymer backbone chain;

and having second repeating units of the formula ##STR9## where,independently for each such second repeating unit: X₃ and X₄ areindependently O or NR' and R' is independently H, hydrocarbyl,substituted hydrocarbyl or a hydrocarbyl derivative, includinghetero-atom containing constituents; R₅, R₆, R₇ and R₈ combined have atleast four carbon atoms; and Z₃ and Z₄ are each independently one ormore constituent group (e.g., hydrogen, hydrocarbyl, oxygen, etc.)extending from the polymer backbone chain and being covalently bonded toa tetravalent carbon atom in the polymer backbone chain, at least one ofZ₃ and Z₄ being an oxygen that forms a carbonyl group with theassociated carbon atom in the polymer backbone chain.

First and second repeating units can be present in the polymer in anyfashion, including in random, alternating and block configurations. Asused herein, hydrocarbyl refers to any constituent group having onlyhydrogen and carbon atoms, including aliphatic, aromatic, cyclic,noncyclic, saturated, and unsaturated constituents.

Polymers of the materials of the present invention are generallyreferred to herein as polydioxaneones. It will be recognized, however,that when any of X₁, X₂, X₃ or X₄ are NR, then the polymer may containamide linkages characteristic of polyamino acids. As used herein,polydioxaneone generally refers to polymers having repeating unitscharacteristic of monomers of dioxaneones, or the nitrogen-containinganalogues thereof. Dioxaneone as used herein is in a general context torefer to a class of compounds having a dioxane ring, or anitrogen-containing analogue ring thereof, and having one or morecarbonyl oxygens pendant from that ring. Preferably, at least one of X₁and X₂ and at least one of X₃ and X₄ is oxygen. When all of X₁, X₂, Z₁and Z₂ are oxygen, the first repeating unit would be characteristic of arepeating unit derived from a dioxanedione monomer, a particular type ofdioxaneone having two carbonyl groups. Likewise, when all of X₃, X₄, Z₃and Z₄ are oxygen, the second repeating unit would be characteristic ofpolymerization of a dioxanedione. Specific examples of dioxanedionesinclude, for example, lactide, glycolide and other cyclic diesters ofα-hydroxycarboxylic oxides. Polymers having repeating unitscharacteristic of dioxanedione monomers can be referred to morespecifically as polydioxanediones. As used herein, polydioxanedioneincludes nitrogen-containing analogues, having nitrogen rather thanoxygen, as one or more of X₁, X₂, X₃ and X₄ in the polymer backbone.Likewise, as used herein, dioxanedione includes nitrogen analogues, suchas, for example, dilactams.

In one embodiment, first repeating units have the formula ##STR10##where, independently for each such first repeating unit: X₁ and X₂ areindependently O or NR' and R' is independently H or hydrocarbyl; R₁ andR₂ combined have at most one carbon atom; and R₃ and R₄ combined have atmost one carbon atom.

In one embodiment, second repeating units are of the formula: ##STR11##where, independently for each such second repeating unit: X₃ and X₄ areindependently O or NR' and R' is independently H or hydrocarbyl; and R₅,R₆, R₇ and R₈ combined have at least four carbon atoms.

In one embodiment, the materials of the present invention comprise apolymer having one or more repeating units in addition to the first andsecond repeating units. For example, such additional repeating unitscould be derived from additional dioxaneone monomers or from othermonomers capable of polymerization with dioxaneones, including lactones,such as β-butyrolactone, γ-butyrolactone, γ-valerolactone,δ-valerolactone, ε-caprolactone, lactams, epoxides, glycols, succinicacid, tartaric acid, mandelic acid, benzylic acid, and others. Thepolymers could, therefore, be copolymers containing in excess of twocomonomers. Particularly preferred as additional repeating units arethose representative of polymerization of glycols (also known asdihydric alcohols or diols). For example, blocks of such glycols couldbe added into a polymer having first and second repeating units byadding the glycols to a reactive bath following polymerization to formthe first and second repeating units. Any glycol, such as ethylene orpropylene glycol could be used.

The polymers may be plasticized using external plasticizers. In apreferred embodiment, however, the polymer is substantially free of anyexternal plasticizer. Rather, the first repeating units and the secondrepeating units are selected to provide the desired physical properties,thereby eliminating the need for external plasticizers and associatedcosts and complexities of using the same. Not to be bound by theory, itis believed that second repeating units impart flexibility into thecomposition by breaking up the structural regularity otherwise impartedby the first repeating unit, thereby providing the possibility for anamorphous polymer with a substantial amount of internal freedom.

In one embodiment, first repeating units comprise greater than 50 weightpercent of the polymer, preferably from about 50 weight percent to about99 weight percent of the polymer, more preferably from about 80 weightpercent to about 99 weight percent of the polymer still more preferablyfrom about 90 weight percent to about 99 weight percent of the polymer,and most preferably from about 90 weight percent to about 97 weightpercent of the polymer.

In one embodiment, the second repeating units comprise less than 50weight percent of the polymer, preferably from about 1 weight percent toabout 50 weight percent of the polymer, more preferably from about 1weight percent to about 20 weight percent of the polymer, still morepreferably from about 1 weight percent to about 10 weight percent of thepolymer, and most preferably from about 3 weight percent to about 10weight percent of the polymer.

In an embodiment the first reacting units have a molecular weight lessthan about 145. Such first repeating units could be derived, forexample, from polymerization of lactide and/or glycolide monomers.

In one embodiment, second repeating units are derived frompolymerization of tetramethyl glycolide. In another embodiment, secondrepeating units are derived from polymerization of the cyclic diester ofα-hydroxyisovaleric acid. In another embodiment, second repeating unitsare derived from polymerization of the cyclic diester ofα-hydroxycaproic acid. In another embodiment, second repeating units arederived from polymerization of the cyclic diester of α-hydroxyisocaproicacid. In yet another embodiment, the second repeating units are derivedfrom polymerization of the cyclic diester of α-hydroxyoctanoic acid. Itwill be recognized by those skilled in the art that the hydrocarbyl sidechain in the branched isomers of α-hydroxyisovaleric acid andα-hydroxyisocaproic acid could take one of multiple forms. In oneembodiment, such branched isomers comprise a mixture of two or more ofthose possible for such an iso-acid compound.

In one particularly preferred embodiment, first repeating units arederived from polymerization of lactide and second repeating units arederived from monomers selected from the group consisting of tetramethylglycolide, the cyclic diester of α-hydroxyisovaleric acid, the cyclicdiester of α-hydroxycaproic acid, the cyclic diester ofα-hydroxyisocaproic acid, the cyclic diester of α-hydroxyoctanoic acid,and combinations thereof.

The constituents R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ may be any organicconstituents, but preferably are hydrocarbyl or hydrogen. R' ispreferably hydrogen or hydrocarbyl.

In one embodiment, at least one of R₅ and R₆ and at least one of R₇ andR₈ are hydrocarbyl radicals having from two to three carbon atoms. Inanother embodiment, at least one of R₅, R₆, R₇ and R₈ is a hydrocarbylradical having from 4 carbon atoms to about 24 carbon atoms, preferablyfrom 4 carbon atoms to about 16 carbon atoms, and more preferably from 4carbon atoms to about 10 carbon atoms. In one preferred embodiment, thetotal number of carbon atoms in R₅, R₆, R₇, and R₈ combined is at least5, and more preferably is from 5 to about 12. In one embodiment, atleast one of R₅ and R₆ and at least one of R₇ and R₈ is a saturatedhydrocarbyl radical. In a preferred embodiment, R₅, R₆, R₇ and R₈ areeach independently either hydrogen or hydrocarbyl.

In one embodiment, one of R₅ and R₆ is isopropyl and the other ishydrogen, and one of R₇ and R₈ is isopropyl and the other is hydrogen.In another embodiment, one of R₅ and R₆ is propyl and the other ismethyl, and one of R₇ and R₈ is propyl and the other is methyl.

In one embodiment, the constituents R₅ and R₆ are the same as theconstituents R₇ and R₈, such as would be the case if the secondrepeating units were derived from a symmetrically substituteddioxanedione. In another embodiment, the total number of carbon atoms inR₅ and R₆ combined is different than the number of carbon atoms in R₇and R₈ combined, such as would be the case if the second repeating unitswere derived from an unsymmetrically substituted dioxanedione.

In one embodiment, the polymers of the present invention have aweight-average molecular weight of greater than about 30,000, preferablygreater than about 70,000 and more preferably greater than about100,000. Although the desired weight-average molecular weight of thepolymer will depend upon the specific product embodiment, as discussedbelow, one generally preferred range is a weight-average molecular offrom about 100,000 to about 500,000, and more preferably from about150,000 to about 250,000.

Monomers

Monomers useful for preparing first repeating units and second repeatingunits of polymers, from which materials of the present invention aremade, can be any monomers that, when polymerized, result in the firstand second repeating units respectively. Such monomers could be, forexample, α-hydroxycarboxylic acids or esters, salts or amides thereof.Preferably, however, the monomers used to prepare the first repeatingunits and second repeating units are cyclic compounds, such asdioxaneones or nitrogen-containing analogues thereof. Preferably, firstmonomers result in first repeating units upon polymerization and secondmonomers result in second repeating units upon polymerization.

In one embodiment, cyclic compounds used as monomers to prepare polymersof the present materials comprise first monomers of the formula##STR12## where, independently for each such first monomer: X₅ and X₆are independently O or NR' and R' is independently H, hydrocarbyl,substituted hydrocarbyl or a hydrocarbyl derivative, includinghetero-atom containing constituents; R₉, R₁₀ and Z₅ combined have atmost one carbon atom; R₁₁, R₁₂ and Z₆ combined have at most one carbonatom; and Z₅ and Z₆ are each independently one or more constituent group(hydrogen, hydrocarbyl, oxygen, etc.) extending from the ring and beingcovalently bonded to a tetravalent carbon atom in the ring, at least oneof Z₅ and Z₆ being an oxygen that forms a carbonyl group with theassociated carbon atom in the ring;

and comprise second monomers of the formula ##STR13## where,independently for each such second monomer: X₇ and X₈ are independentlyO or NR' and R' is independently H, hydrocarbyl, substituted hydrocarbylor a hydrocarbyl derivative, including hetero-atom containingconstituents; R₁₃, R₁₄, R₁₅ and R₁₆ combined have at least four carbonatoms; and Z₇ and Z₈ are each independently one or more constituentgroup (hydrogen, hydrocarbyl, oxygen, etc.) extending from the ring andbeing covalently bonded to a tetravalent carbon atom in the ring, atleast one of Z₇ and Z₈ being an oxygen that forms a carbonyl group withthe associated carbon atom in the ring.

When both Z₅ and Z₆ are carbonyl oxygens, then the first monomers aredioxanediones, or nitrogen-containing analogues thereof. When both Z₇and Z₈ are carbonyl oxygens, then the second monomers are dioxanediones,or nitrogen-containing analogues thereof. R' is preferably hydrogen orhydrocarbyl.

In one embodiment, first monomers are dioxanediones, ornitrogen-containing analogues thereof, of the formula ##STR14## where,independently for each such first monomer: X₅ and X₆ are independently Oor NR' and R' is independently H or hydrocarbyl; R₉ and R₁₀ combinedhave at most one carbon atom; and R₁₁ and R₁₂ combined have at most onecarbon atom.

In one embodiment, second monomers comprise dioxanediones, ornitrogen-containing analogues thereof, of the formula ##STR15## where,independently for each such second monomer: X₇ and X₈ are independentlyO or NR' and R' is independently H or hydrocarbyl; and R₁₃, R₁₄, R₁₅ andR₁₆ combined have at least four carbon atoms.

Preferably, at least one of X₅ and X₆ and at least one of X₇ and X₈ isoxygen. R₉, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, R₁₅ and R₁₆ can be the same ordifferent from each other and can be any organic constituent such ashydrogen, hydrocarbyl, substituted hydrocarbyl, saturated hydrocarbyl,and others, including hetero-atom containing constituents. Preferably,R₉, R₁₀, R₁₁ and R₁₂ are hydrogen or hydrocarbyl, and if hydrocarbyl aremore preferably saturated hydrocarbyl. R₁₃, R₁₄, R₁₅ or R₁₆ could be,for example, a furfural-based constituent, a vinyl-based constituent, aconstituent having an aromatic ring. R₁₃ and R₁₄ or R₁₅ and R₁₆,respectively, could connect to form a single constituent, such as acyclic constituent in which the ring of the constituent includes acarbon atom of the dioxane ring, such as in a spiro compound, such as,for example: ##STR16## Preferably, however, R₁₃, R₁₄, R₁₅ and R₁₆ arehydrogen or hydrocarbyl, and if hydrocarbyl are more preferablysaturated hydrocarbyl.

In one embodiment, first monomers have a molecular weight less thanabout 145. Such first monomers could be, for example, lactide, and/orglycolide.

In one embodiment, second monomers comprise tetramethyl glycolide. Inanother embodiment, second monomers comprise the cyclic diester ofα-hydroxyisovaleric acid. In another embodiment, second monomerscomprise the cyclic diesters of α-hydroxycaproic acid. In anotherembodiment, second monomers comprise the cyclic diester ofα-hydroxyisocaproic acid. In another embodiment, second monomerscomprise the cyclic diester of α-hydroxyoctanoic acid.

In one embodiment, at least one of R₁₃ and R₁₄ and at least one of R₁₅and R₁₆ are hydrocarbyl radicals having from two to three carbon atoms.In another embodiment, at least one of R₁₃, R₁₄, R₁₅ and R₁₆ is aradical having from 4 carbon atoms to about 24 carbon atoms, preferablyfrom about 4 carbon atoms to about 16 carbon atoms, and more preferablyfrom about 4 carbon atoms to about 10 carbon atoms. In one preferredembodiment, the total number of carbon atoms in R₁₃, R₁₄, R₁₅ and R₁₆combined is at least 5 and more preferably from 5 to about 12. In oneembodiment, at least one of R₁₃ and R₁₄ and at least one of R₁₅ and R₁₆are saturated hydrocarbyl radicals.

In one embodiment, one of R₁₃ and R₁₄ is isopropyl and the other ishydrogen, and one of R₁₅ and R₁₆ is isopropyl and the other is hydrogen.In another embodiment, one of R₁₃ and R₁₄ is propyl and the other ismethyl, and one of R₁₅ and R₁₆ is propyl and the other is methyl.

In one embodiment, the constituents R₁₃ and R₁₄ are the same as theconstituents R₁₅ and R₁₆, such as would be the case, for example, for asymmetrically substituted dioxanedione. In another embodiment, the totalnumber of carbon atoms in R₁₃ and R₁₄ combined is different than thenumber of carbon atoms in R₁₅ and R₁₆ combined, such as would be thecase, for example, for an unsymmetrically substituted dioxanedione.

In one embodiment, first monomers comprise from about 50 weight percentto about 99 weight percent of the total monomers from which the polymeris prepared, such as, for example, in a monomer mixture comprising bothfirst monomers and second monomers. Preferably, first monomers comprisefrom about 80 weight percent to about 99 weight percent of the totalmonomers, more preferably from about 90 weight percent to about 99weight percent of the total monomers, and most preferably from about 90weight percent to about 97 weight percent of total monomers.

In one embodiment, second monomers comprise from about 1 weight percentto about 50 weight percent of the total monomers from which the polymeris prepared. Preferably, second monomers comprise from about 1 weightpercent to about 20 weight percent of the total monomers, morepreferably from about 1 weight percent to about 10 weight percent of thetotal monomers, and most preferably from about 3 weight percent to about10 weight percent.

Preparation of Monomers

Cyclic compounds that may be used as monomers for manufacturing thepolymers of the present materials can be prepared using any suitablemethod. Dioxanedione monomers, or nitrogen-containing analogues thereof,are preferably prepared directly from noncyclic α-hydroxycarboxylic acidesters or nitrogen-containing analogues, such as α-hydroxyamides, orfrom derivatives, such as salts, of either, thereby avoiding problemsinherent with conventional backbiting methods. Such esters, amides andderivatives thereof can be prepared from base molecules, such as forexample, α-hydroxycarboxylic acids and/or α-hydroxyamides. A moredetailed discussion of methods useful for producing cyclic compounds,such as dioxaneones, and particularly dioxanediones, ornitrogen-containing analogues thereof, directly from noncyclic esters,or nitrogen-containing analogues such as amides, is provided inco-pending, commonly assigned U.S. application Ser. No. 07/854,559 for"Method to Produce Cyclic Esters", by Benecke et al., filed Mar. 19,1992, and U.S. application Ser. No. 08/128,797 for "Method to ProduceCyclic Esters", by Verser et al., filed on even date herewith, both ofwhich are incorporated herein in their entireties.

To better describe the production of cyclic compounds such asdioxanediones, or nitrogen-containing analogues thereof, directly fromthe noncyclic ester species, the following nomenclature, as more fullyexplained in U.S. application Ser. No. 07/854,559, may be used. Basemolecules, such as α-hydroxycarboxylic acids, α-hydroxyamides, and saltsand other derivative compounds (e.g., esters, ethers and salts withother than base molecules) of the foregoing are referred to as Y₁ A. Y₂A refers to a noncyclic, linear dimer, such as, for example, a moleculeformed by a single reaction between any two Y₁ A molecules to form anoncyclic, straight chain, dimer having an ester or amide linkage. Forexample, the molecule formed by a single esterification of twoα-hydroxycarboxylic acid base molecules would be a Y₂ A. A Y₃ A refersto a noncyclic, linear trimer of base molecules having ester and/oramide linkages. Y₄ A refers to a noncyclic, linear tetramer having esterand/or amide linkages and Y_(n) A refers to a noncyclic, linear n-mer.It should be recognized that Y₂ A is not limited by its method offormation, and could, for example, be formed by depolymerization, or byanother decomposition reaction, of a larger oligomeric molecule, such asfrom a Y₃ A or a Y₄ A or a larger Y_(n) A. Likewise, any Y_(n) A couldbe a depolymerization product of a larger oligomer. As used herein, YAwithout subscript generally denotes at least one of and generally amixture of two or more of Y₁ A, Y₂ A, Y₃ A, and Y₄ A, or a solutionthereof, When Y is substituted by L or G, specific correspondingcompounds based on lactic acid and glycolic acid, respectively, aremeant. For example, LA refers to L₁ A, L₂ A, L₃ A, L₄ A, etc. YD refersgenerically to a dioxanedione, or a nitrogen-containing analog thereof.LD refers specifically to lactide. As used herein, an amide refers tomolecules that have an acyl group, being the nitrogen-containinganalogue of a carboxyl group such as would be the case for anitrogen-containing analogue of a carboxylic acid, and also moleculesthat have an amide linkage, such as would be the case for anitrogen-containing analogue of an ester linkage.

A cyclic compound of dioxanedione, or a nitrogen-containing analoguethereof, derived from Y₁ A is produced by providing a compound mixturecontaining components including but not limited to YA, and treating thefeedstream to form cyclic compounds which may be used as monomers forpolymers of the present materials, as previously described. Not to bebound by theory, it is believed that the cyclic ester, ornitrogen-containing analogue, is formed primarily directly from a lineardimer, i.e., from Y₂ A. Under certain reaction conditions, however, itis believed that Y₃ A and Y₄ A also contribute to dioxanedioneformation. As used herein, forming the dioxanedione primarily directlyfrom Y₂ A refers to a reaction in which Y₂ A, such as Y₂ A alreadypresent in the feedstream or Y₂ A formed by an esterification reactionbetween two Y₁ A molecules, is converted to a cyclic compound ofdioxanedione or a nitrogen-containing analogue thereof by ring-closingesterification or by a ring-closing formation of an internal amidelinkage. That is, the cyclic compound is not formed by backbiting ofpolyester chains, as described in the prior art when a dioxanedione isformed from Y₅ A or greater.

In one embodiment, cyclic esters or nitrogen-containing analoguesthereof such as amides, including dioxanediones, are prepared from anoncyclic ester or nitrogen-containing analogue thereof, by treatmentincluding removal of water from a compound mixture including reactivecomponents and an organic or silicon-based solvent.

In this embodiment, water initially in the compound mixture is removedrapidly leading to an essentially dehydrated feedstream having a waterconcentration of less than about 2 wt %. Water formed by theesterification reactions is preferably removed essentially as it isformed. In particular, water is typically removed at a rate such thatthe concentration of water in the treated compound mixture is less thanabout 2 wt %, more preferably less than about 1 wt %, and even morepreferably less than about 0.5 wt %.

Water can be removed from a compound mixture by a variety of methods,including, but not limited to: evaporation; a solvent-based reactionprocess, such as a reactive distillation process; removal of water as anazeotrope from a feedstream in which the reactive components are dilutedin a solvent which forms an azeotrope with water; adding a water-getterwhich preferentially reacts with water; using molecular sieves orpartitioning (e.g., osmotic) membranes; using anhydrous salts that formhydrated crystals with water; contacting the feedstream with waterabsorptive materials, such as polysaccharides or silica.

As noted above, the reaction is preferably conducted in a solvent.Preferably, the reactive components of the compound mixture are presentin dilute concentration in a solvent. For example, the concentration ofYA can be less than about 25% by weight of a feedstream. Preferably, YAspecies are 100% soluble in the solvent at reaction conditions.

Preferably, the solvent is relatively polar because it is believed thatmore polar solvents, such as anisole, favor the selective formation ofYD over Y₅ A and higher oligomers. Suitable solvents for use in thepresent invention can include aromatic solvents, aliphatic solvents,ethers, ketones, silicon-based solvents and halogenated solvents.Preferred solvents are aromatic solvents.

Specific solvents of the present invention include 2-butanone,2-heptanone, 2-hexanone, 2-pentanone, acetone, anisole, butyl ether,ethyl ether, isopropyl ether, methyl-phenyl ether, benzene, cumene,m-xylene, o-xylene, p-xylene, toluene, cyclohexane, heptane, hexane,nonane, octane, 1-pentene, 2-octanone, dimethyl sulfoxide, phenetole,4-methyl anisole, 1,3-dimethoxybenzene, 1,2-dimethoxybenzene,1,4-dimethoxybenzene, mesitylene, chlorobenzene, 1,2-dichlorobenzene,1,3-dichlorobenzene, 1,4-dichlorobenzene, 2-chlorotoluene,4-chlorotoluene, veratrole, and 3-chlorotoluene. Preferred solventsinclude toluene, xylene, anisole, phenetole, 4-methyl anisole,1,3-dimethoxy benzene, and mesitylene. Particularly preferred solventsof the present invention include xylene, anisole and 4-methyl anisole.

Substituted aromatic solvents are particularly preferred for the presentinvention. Such solvents are typically polar and thus, provide highselectivity. Also preferred are di-substituted aromatics, such as4-methyl anisole.

The cyclic compound formed by the above-described process can berecovered and purified, for example, by crystallization, solventextraction, distillation, membrane partitioning, washing with solvent,chromatography, sublimation, and combinations thereof. Preferably, thecyclic compound is a dioxanedione, or a nitrogen-containing analoguethereof, all as previously described.

The role played by water in the present process can be appreciated byreference to the following equilibrium reactions:

    2Y.sub.1 A⃡Y.sub.2 A+H.sub.2 O,

    Y.sub.2 A⃡YD+H.sub.2 O,

    Y.sub.1 A+Y.sub.2 A⃡Y.sub.3 A+H.sub.2 O,

    etc.

Thus, it will be observed that Y₁ A is in equilibrium with higheroligomers of Y₁ A, cyclic esters and water. By removing water, thereactions are driven to the right and, conversely, by adding water thereactions are driven to the left.

Different monomers useful in preparing polymers for the presentmaterials, as previously discussed, can be prepared individually andmixed together for polymerization, or they can be prepared together.When prepared individually, for example, a first monomer could beprepared from first YA species (e.g., from a first Y₂ A). A second,different monomer could be separately prepared from second YA species(e.g., from a second Y₂ A). The first and second monomers, preferablyfollowing purification of each, could then be mixed together andcopolymerized to form a polydioxaneone useful in making the materials ofthe present invention.

In another embodiment, a first monomer and a second monomer could bothbe prepared from a single feed. The feed could contain, for example, twodifferent base molecule species, preferably with one present in a muchlower concentration than the other. In such a feed mixture, the Y₂ Awould comprise first linear dimers representative of two first basemolecules and would also comprise second two linear dimersrepresentative of one of a first base molecule and one of a second basemolecule. If the concentration of first base molecules is sufficientlyhigh compared to second base molecules, then the feed would not compriseappreciable amounts of Y₂ A other than the two already described. Themonomers produced would then comprise primarily first monomers that aresymmetrically substituted dioxanediones, or nitrogen-containinganalogues thereof, being the cyclic compounds representative of two ofthe first base molecule. The monomers produced would also comprise asmaller amount of second monomers that are unsymmetrically substituteddioxanediones, or nitrogen-containing analogues thereof, being thecyclic compounds representative of one of a first base molecule and oneof a second base molecule. For example, lactic acid (i.e.,α-hydroxypropanoic acid) and α-hydroxyoctanoic acid could be mixed asfirst and second base molecules in a feed. First monomers would then bea cyclic diester representative of two lactic acids (i.e., lactide) andsecond monomers would then be a cyclic diester representative of onelactic acid and one α-hydroxyoctanoic acid. This process could also beused to make more than two different dioxanedione monomers together.

Additional information relating to internally modified polymercompositions can be found in co-pending, commonly assigned U.S. patentapplication Ser. No. 08/127,907 for "DEGRADABLE POLYDIOXANEONE-BASEDMATERIALS," by Lipinsky et al., filed on even date herewith, which isincorporated by reference herein in its entirety.

PREPARATION OF POLYMERS

The polymer of the present materials can be prepared by a variety ofpolymerization techniques. The polymerization reaction is conducted inthe liquid phase in a closed, evacuated vessel. Alternatively, thepolymer can be prepared at atmospheric pressure with the polymerizationmixture blanketed by an inert gas such as, for example, nitrogen. If thepolymerization reaction is conducted in the presence of oxygen or water,such as would be the case for air, some discoloration or chaintermination or catalyst deactivation can occur in the final polymer witha resulting decrease in molecular weight and tensile strength.

Typically, the polymerization is conducted above the melting point ofthe monomers and below a temperature at which degradation of theresulting polymer occurs. The catalysts used in the polymerizationreaction of the present invention can be metal salts and esters ofcarboxylic acids containing up to 18 carbon atoms. Examples of suchacids are formic, acetic, propionic, lactic, butyric, valeric, caproic,2-ethylhexanoic, caprylic, pelargonic, capric, lauric, myristic,palmitic, stearic, and benzylic acids. For example, good results can beobtained in the polymerization of lactide using stannous acetate orstannous caprylate.

The catalyst is used in normal catalytic amounts for polymerization. Forexample, a stannous 2-ethylhexanoate catalyst concentration in a rangeof about 0.001 to about 2 percent by weight, based on total weight ofthe monomers or comonomers, is suitable for polymerization of lactide. Acatalyst concentration in the range of about 0.01 to about 1.0 percentby weight is preferred. Particularly preferred is a catalystconcentration in the range of about 0.02 to about 0.5 percent by weight.The exact amount of catalyst in any particular case depends to a largeextent upon the catalyst employed and the operating variables, includingtime, temperature and the desired rate of reaction.

The reaction time of the polymerization process is dependent on variousreaction variables, including reaction temperature, polymerizationcatalyst, amount of catalyst, degree of mixing, and whether a solvent isused. The reaction time can vary from a matter of minutes to a period ofhours or days, depending upon the particular set of conditions which isemployed. Heating of the mixtures of monomers or comonomers is continueduntil the desired level of polymerization is attained. For example, theextent of polymerization can be determined by analysis for residualmonomers. In general, it is preferred to conduct the polymerization inthe absence of impurities which contain active hydrogen since thepresence of such impurities tends to deactivate the catalyst and/orincrease the reaction time. It is also preferred to conduct thepolymerization under substantially anhydrous conditions.

The polymer of the present invention can be prepared by bulkpolymerization, suspension polymerization or solution polymerization.The polymerization can be carried out in the presence of an inertnormally-liquid organic vehicle such as, for example, aromatichydrocarbons such as benzene, toluene, xylene, ethylbenzene and thelike; oxygenated organic compounds such as anisole, dimethyl and diethylethers of ethylene glycol; normally-liquid saturated hydrocarbonsincluding open chain, cyclic and alkyl-substituted cyclic saturatedhydrocarbons such as hexane, heptane, cyclohexane, decahydronaphthaleneand the like.

The polymerization process can be conducted in a batch, semi-continuous,or continuous manner. In preparing the monomeric reactants and catalystsfor subsequent polymerization, they can be admixed in any orderaccording to known polymerization techniques. Thus, the catalyst can beadded to one comonomeric reactant. Thereafter, the catalyst-containingcomonomer can be admixed with another comonomer. In the alternative,comonomeric reactants can be admixed with each other. The catalyst canthen be added to the reactant mixture. If desired, the catalyst can bedissolved or suspended in an inert, normally-liquid organic vehicle. Ifdesired, the monomeric reactants either as a solution or a suspension inan inert organic vehicle can be added to the catalyst, catalyst solutionor catalyst suspension. Alternatively, the catalyst and comonomericreactants can be added to a reaction vessel simultaneously. The reactionvessel can be equipped with a conventional heat exchanger and/or mixingdevice. The reaction vessel can be any equipment normally employed inthe art of making polymers. One suitable vessel, for example, is astainless steel vessel.

MATERIAL TYPES

As discussed above, the present invention is directed to a variety ofproducts made of degradable materials. The degradable materials includethe polymer and modifier. The various materials of the present inventionhave varying chemical and physical characteristics which are relevant totheir intended uses. The materials of the present invention include thefollowing types: films, fibers, molded products, laminates, foams,powders, nonwovens, adhesives, coatings, extruded profiles, beads, andcolorant carriers.

Film material of the present invention is made from compositions asdescribed above. The term film, as used herein, refers to a materialtype which is a film in its final product configuration and does notrefer to intermediate source materials which are subsequently processedinto non-film products. The term film includes material commonlyidentified as a film with thicknesses of less than about 20 mil and alsois intended to include materials which may also be termed sheets,including materials with thicknesses up to about 50 mil. Such films canbe prepared to simulate the properties of common materials, such aspolyethylenes, polystyrenes, and vinyls. The desired molecular weightand distribution for each application is achieved by adjustment of thepolymerization conditions and by post-polymerization processing. Choicesand percentages of modifier(s) affect flexibility and processingtemperatures as well as the degradation rate. Such films can be producedby a variety of known processes. For example, films can be prepared bycompression molding processes. Suitable films can also be prepared byextrusion processes, including blown film processes and by castingsolutions of the polymer composition and then recovering the solvent.Thermal annealing and quenching are two methods that control themorphology of the film to emphasize selected properties. Quenching asused herein indicates that the temperature of a material is droppedrapidly to prevent extensive crystallization of the polymer.Crystallization of polymers is a slow process, requiring minutes tohours to fully accomplish. When crystallization is desired, thetemperature is held above the glass-transition temperature, T_(g), forsome time to allow the molecules to order themselves into extensivecrystalline lattices. This process is called annealing. When cooledrapidly from an amorphous melt, the polymer does not have the timerequired for crystallization and remains largely amorphous. The timerequired to quench depends on the thickness of the sample, its molecularweight, melt viscosity, compositions, and its T_(g). Note that meltviscosity and T_(g) are lowered by plasticization which facilitatesquenching. Thin films obviously cool very quickly because of their highsurface-to-volume ratio while thicker films cool more slowly with theirgreater thicknesses. Regular structures such as homopolymers order moreeasily and crystallize more quickly than more random structures such asa copolymer.

Quenching to an amorphous state requires that the polymer or copolymerin an amorphous melt is rapidly cooled from its molten state to atemperature below its T_(g). Failure to cool rapidly allows spheruliticcrystallinity to develop, that is, crystalline domains of submicron tomicron size. The latter scatters light and the polymer specimens becomeopaque. These crystalline forms have improved stability to heatdistortion. This spherulitic crystallinity is often called short rangeorder long-range disorder since the crystallites are separated byamorphous regions. However, the crystallites act as pseudo crosslinks tomaintain dimensional stability above the T_(g) but below their meltingpoints. Alternatively stability to heat distortion can be obtained byorienting a crystallizable amorphous polymer. Here, the polymermolecules are stretched to allow some long-range ordering, then "heatset" to permit the ordering to complete, that is, given some time toanneal. The amorphous polymer is thereby crystallized into a differentorder, called long-range order, short-range disorder. Transparency andresistance to heat distortion are favored using this type of order.

Films of the present invention can be oriented or not and can beshrinkable or not. Orientation refers to stretching a film in at leastone direction which allows for alignment and ordering of the polymermolecules along the direction of stretching. The stretching can be 2, 3or 4 times the original length of film in the direction of stretching.Orienting can be uniaxial, which is typically in the direction the filmtravels as it is processed. Alternately, orienting can be biaxial whichis typically in the direction the film travels as it is processed and ina second direction transverse to the first. Orientation is conducted ata film temperature above the T_(g) of the film and below its meltingpoint. Biaxially oriented films are useful as shrinkable films in shrinkwrap packaging.

Biaxially oriented films can be dimensionally stabilized to heat byannealing under restraint after drawing at a temperature above the T_(g)and below the melting point. This procedure allows internal tension inthe film to relax and upon cooling the film is non-shrinkable.

As noted above, films of the present invention can be prepared having avariety of product characteristics. Such films can have polystyrene-likeproperties, low density polyethylene-like properties, high densitypolyethylene-like properties, polypropylene-like properties andpolyvinyl chloride-like properties. Polystyrene-like films of thepresent invention typically have a weight average molecular weightbetween about 100,000 and 500,000, a T_(g) of between about 100° C. and105° C. when not oriented and a form-stability to heat when oriented atbetween about 70° C. to about 150° C., a tensile strength of betweenabout 6,000 psi and about 8,000 psi when not oriented, whichapproximately doubles when oriented 3X to 5X, a Shore D hardness ofbetween about 80 and about 90, an elongation to break of about 2% toabout 4% when not oriented, or 4% to 40% when oriented, an elasticmodulus of greater than about 250,000 psi, and typically are transparentand are semicrystalline and degrade under ambient conditions in about 6to about 24 months. Low density polyethylene-like film materials of thepresent invention typically have a weight average molecular weight fromabout 100,000 to about 500,000, a T_(g) of about -20° C., a tensilestrength of between about 1,500 psi and about 3,000 psi, a Shore Dhardness of about 50, an elongation to break to about 150% to about1,200%, an elastic modulus of between about 10,000 psi and about 50,000psi, and is sometimes transparent, is not crystalline, and is degradableunder ambient conditions in about 3 to about 12 months. High densitypolyethylene-like materials of the present invention typically have aweight average molecular weight of between about 100,000 and about500,000, a T_(g) of about room temperature to about -120° C., a tensilestrength of between about 2,500 psi to about 4,000 psi, a Shore Dhardness of between about 50 and about 60, an elongation to break ofbetween about 50% and about 500%, an elastic modulus of between about50,000 psi and about 125,000 psi, and is sometimes transparent, iscrystalline, and is degradable under ambient conditions in from about 6to about 24 months. Polypropylene-like films of the present inventiontypically have a weight average molecular weight of between about100,000 and about 500,000, a Tg of about 0° C., a tensile strength ofbetween about 4,000 and about 6,000, a Shore D hardness of about 70, anelongation to break of between about 100% and about 600%, an elasticmodulus of between about 135,000 psi and about 200,000 psi, and issometimes transparent, is crystalline, and is degradable under ambientconditions in from about 6 months to about 24 months. Polyvinylchloride-like films of the present invention typically have a weightaverage molecular weight of between about 100,000 and about 500,000, aT_(g) of below room temperature, a tensile strength of between about 300psi and about 500 psi, a Shore D hardness of between about 10 and about90, an elongation to break of between about 5% and about 500%, anelastic modulus of between about 500 psi and about 250,000 psi, and issometimes transparent, is not crystalline, and is degradable underambient conditions in from about 6 months to about 24 months.

A fiber-type material of the present invention is prepared by extrudinga thin filament through a spinneret, and allowing the filament to coolprior to being rolled onto a spool. In this manner, the filament ismaintained as a fiber. Polymers used for fibers are generally classifiedinto two types, textile fibers used for products such as clothing,fabrics, carpets, draperies and industrial fibers used for products suchas tire cords, reinforcements for composite applications, industrial usefabrics (e.g., sails, nets, ropes and tarps). Fibers used in textilesshould be either dyeable or able to be colored in the melt by pigments.Moisture absorbances can range from about 0% to about 20% for mosttextile fibers. The polymers used in textile fibers should be resistantto the acidic or basic conditions encountered in dying, scouring (a typeof laundering process) and finishing by applying, for example, soilresistance, antistatics and permanent press.

Typical textile fibers have breaking strengths from about 14 KPSI toabout 87 KPSI and breaking elongations from between about 5% to about60%. Industrial fibers generally have significantly higher breakingstrengths of from about 100 KPSI to about 500 KPSI, have higherstiffness (modulus) and lower breaking elongations from about 1% toabout 30%. Polymer molecular weight distributions for fiber gradepolymers are generally narrow from about 2 to about 5 and weight averagemolecular weights from about 30,000 MW for condensation type polymers(e.g., nylons and terephthalate based polyesters) to about 150,000 MWfor chain type polymers (e.g., polyolefins).

Molded product material of the present invention is made fromcompositions as described above. Molded product material can be made bya variety of processes, including blow molding, injection molding, openpot molding, and thermoforming. Blow molding is employed to make hollowshapes, especially packaging containers. In an extrusion embodiment ofthis process, a parison is made first and then expanded to the walls ofthe mold cavity. The degradable polymer composition is tailored to meetextrusion blow molding processing requirements by adjustment ofcomonomer ratio, molecular weight of the polymer product, andchoice/percentage of modifier. These processing requirements arereconciled with the end use requirements with regard to shelf life,strength, speed of onset of degradation, and other parameters. Molecularweights of over 100,000 and as high as 500,000 are desirable for theseapplications. There are trade-offs in molecular weight and percentmodifier such that flexible bottles can be made by use of polymericplasticizers with moderate molecular weight degradable polymers.Polymeric plasticizers are not extracted into the liquid contents ofcontainers, and the flexibility of the package renders it moreimpact-resistant.

Injection molding of thermoplastics is accomplished by melting thethermoplastic composition and transferring it into a closed mold cavitywhere it solidifies to conform to the shape of the mold. Injectionmolded products require little or no mechanical work before they arefabricated with other parts into an end use product.

The materials of this invention are highly suitable for injectionmolding because their melting points and morphology can be tailored inmany different ways. Thus, a dense polymer (specific gravity=1.25) canbe blended with less dense plasticizers that can fine-tune theconsistency of the material to be injected. The molecular weights anddistribution of molecular weight can be adjusted. Because the economicsof injection molding usually necessitates short cycle times, relativelylow molecular weights (less than 120,000) are desirable.

Injection molded products of the present invention typically have aweight average molecular weight of between about 50,000 and about150,000 a T_(g) of greater than about 50° C., a tensile strength ofgreater than about 3,000 psi, a Shore D hardness of between about 50 andabout 90, an elongation to break of between about 2% and about 25%, anelastic modulus of between about 100,000 psi and about 400,000 psi, andare sometimes transparent, are semicrystalline, and degradable underambient conditions in from about 6 months to about 24 months.

Similar to injection molding, open pot molding is accomplished bymelting the thermoplastic composition and transferring it into an openmold where it solidifies to conform to the shape of the mold.

Thermoforming is a branch of molding that uses thick films or sheets ofthermoplastic. Because the materials of this invention are especiallyeasy to convert to film or sheet form that have excellent transparency,they are excellent candidates for thermoforming. The sheet must beheated to the point that it is quite flexible and then subjected tovacuum or pressure that presses the sheet against a mold, forming thedesired shape. The plastic memory of these polymer-plasticizercombinations is a useful attribute in drape forming embodiments ofthermoforming.

Another material type of the present invention includes laminates andcoextrudates. Film laminates and coextruded films are compositematerials in which each layer provides functional utility thatcomplements the rest of the structure. The polymer/modifier materials ofthis invention provide degradability, in addition to such functions asstrength, printability, and high transparency. The other layers in thelaminate or coextruded structure can provide temporary protectionagainst moisture or abrasion so that the onset of degradation is delayeduntil after the shelf-life and consumer-use phases have passed. Theother layers may provide essential electrical or other functions thatforce the layer to be nondegradable; however, the adverse environmentalimpact can be reduced by using the polymers of this invention for mostof the weight of the product.

Laminated or coextruded products of the present invention can be used ina variety of functions. For example, many packaging materials can beprepared from laminates or coextrudates. Such packaging materials, forexample, have layers which perform various functions, such as structuralstability, gas permeability, decoration and moisture exclusion. Thepolymer compositions of the present invention, can be used, for example,as a transparent outer protective coating for such a laminate product.

A laminate or coextrudate of the present invention typically has aweight average molecular weight of between about 50,000 and 500,000, aT_(g) below about room temperature, a Shore D hardness of about 20 toabout 70, an elongation to break of greater than about 300%, a tensilestrength of between about 2,000 psi and about 40,000 psi, an elasticmodulus of between about 20,000 and about 700,000 psi, and is notcrystalline, and is degradable under ambient conditions in from about 1month to about 2 years.

A further material type of the present invention includes foams. Foamedthermoplastics have large markets in food packaging. The materials ofthis invention are outstanding candidates for use in these applicationsbecause they can be melted to a high-viscosity material that can beblended with such gases as carbon dioxide or nitrogen for foamextrusion. The viscosity of the melt can be optimized by molecularweight and by modifier content. Typically, the polymer will have amolecular weight of more than 150,000 for foam extrusion. Polymericmodifiers are especially desirable for this foam application because arather stiff bubble is desirable. The solubility (under pressure) ofcarbon dioxide in the polymers of this invention can be exploited tocontrol pore size of bubbles that are produced after cooling.

Foam materials of the present invention typically have a weight averagemolecular weight of between about 50,000 and about 500,000, a T_(g) ofgreater than 50° C., and are semicrystalline and are degradable underambient conditions in between about 6 months to about 24 months.

A further material of the present invention includes spun-bondednonwoven material. The term "spun-bonded nonwoven" refers to materialwhich is prepared by extruding a thin film filament through a spinneretonto a flat cooled surface in an irregular pattern to form a relativelyuniform sheet which is not in a woven pattern. Spun-bonding requiresadherence to a limited range of melt viscosities so that the rovingspinnerets can deliver the appropriate amount of material to the cooledsurface. The detailed response of the polymer melt to the quenching isalso a sensitive processing parameter. Such nonwoven materials typicallyhave high strength characteristics and can be used for envelopes andother similar containers. The polymers of this invention can beoptimized to meet the processing requirements by manipulation of manyvariables, including control of molecular weight and molecular weightdistribution and selection of comonomers. Typically, nonwoven materialhas a high molecular weight and have high elongation. Thus, the fibersare flexible and easily entangled. The nonwoven material can be hard orsoft, absorbent or chemically resistant, depending upon the application.Modifiers play an important role by facilitating the initial bondingamong fibers.

Polymers for spunbonded nonwovens are generally fiber grade typepolymers, since the initial forming process has aspects of fiberspinning. Spinning speeds for the spunbonded filaments is in the 3,000to 6,000 mole per minute range. The polymers should have sufficientthermal stability for steam or heat point bonding. The fabrics,particularly those used in disposable medical or clean room type uses,should be stable to sterilization by, for example, heat or chemicalmeans, such as ethylene oxide. The fabrics also should not have or formlint and should resist fluid and bacterial penetration.

Spunbonded nonwovens generally have base weights of between about 0.8ounces per square yard to about 5 ounces per square yard. Tensilestrengths of the spunbonded nonwoven fabrics range from about 1 poundsto about 150 pounds in the machine or extrusion/fabric laydown direction(MD) and about 1.1 pounds to about 170 pounds in the transverse or crossdirection (XD). Tear strengths range from about 1 pound to about 80pounds in the MD and XD directions. Burst strengths (Mullen) range fromabout 35 KPSI to about 225 KPSI for spunbonded nonwoven fabrics.

A further product type of the present invention includes adhesives. Thepolymer compositions of this invention have considerable utility asadhesives because they can be hot-melt or solvent-based products. Choiceof comonomers and the molecular weight distribution can affect themelting point of the hot melt and its changes in morphology duringtackifying and hardening. The modifiers provide additional dimensions tothe hot melt formulations. In addition to optimizing viscosity, themodifiers can act as a trigger to initiate a gradual degradationprocess. The solvents to be used in the solvent-based adhesives could bethe modifier part of the formulation. The biocompatible modifiers ofthis invention (e.g., acetyl triethyl citrate or lactide) can providethe functions that some solvent based formulations obtained from toxicor flammable solvents.

The polymers of this invention that are to be used in adhesives rangewidely in composition and molecular weight, depending on the specifictype of adhesive and the specific application. The surface properties ofthe substrates to be bonded are of great importance in the choice ofpolymer. For example, a polylactide (M_(w) of about 200,000) wasdissolved in a low boiling solvent and employed to bond together twopieces of wood. A strong bond was formed that lasted for more than twoyears at ambient temperatures in an office environment. Other substratessuch as paper may need only M_(w) of 10,000 to attain a strong bond. Theexcellent compatibility of polylactides and other polymers of thisinvention with substances with solubility parameters that differ widelyamong themselves indicates that these polymers are especially suited tobonding together disparate materials.

Adhesives of the present invention typically have a weight averagemolecular weight of between about 5,000 to about 200,000, a T_(g) ofless than room temperature, a Shore D hardness of about 0.5, anelongation to break of greater than about 300%, an elastic modulus ofless than about 1,000, and are not transparent and are not crystalline.

A further material type of the present invention include variouscoatings. Unlike some films, moldings, and foams, coatings do not haveto be strong enough to be self-supporting. Therefore, an extremely widerange of the polymer composition of this invention can be employed forcoating use. The degradability aspect allows the coating to be atemporary protection of the underlying substrate against abrasion orother harm. The coating can serve many of the functions of a film, inparticular, the coating may serve as a temporary printing surface sothat the label of a container is among the first parts of a package todegrade.

The coating can serve as a binder to incorporate pigments onto writingpapers. This type of usage can facilitate the degradation of the papersubstrate by providing an acid environment for cellulose hydrolysis.

Generally, the polymers to be used on coatings can have a lowermolecular weight and less crystallinity than those that are to be usedin films. Thus, molecular weights may range from 10,000 to 100,000.However, in special circumstances, a combination of high molecularweight with a plasticizer can impart extra strength.

Another material type is an extruded profile material made from theabove described compositions. The term extruded profile, as used herein,refers to a material type which is produced by a polymer compositionbeing forced through a die of a particular shape so that the resultingmaterial has a cross-sectional profile of that shape. The physical andchemical properties vary with the application. For example, polymersused in extruded profiles have a wide range of properties. Theproperties can range from soft medical tubes having strengths between1,000 and 3,000 psi, moduli as low as 1,000 psi, and elongations tobreak up to 2,000% to very rigid structures having strengths as high as12,000 psi, moduli as high as 600,000 psi, and elongation to breaks aslow as 2%. Extruded products typically have good resistance tochemicals.

Molecular weights of extruded profile materials (extrusion or pipegrades) range from 50,000 to 500,000. Tensile strength propertiesgenerally range from 3 KPSI to 8 KPSI with elongations to break from 1to 100%. The chemical properties of the extruded profile materials canvary depending upon the polymer end use applications. For example,polyethylene will have different chemical resistance from polybutyleneor polyvinyl chloride.

Another material type is a bead material made from the compositions ofthe present invention. The bead material is particularly well suited forthe production of products designed for controlled release of chemicals.Molecular weights of bead material typically ranges from 2,000 to350,000.

A further material type is a colorant carrier made from the compositionsof the present invention. The colorant carrier material is particularlyuseful as a carrier for, for example, inks, dyes, pigments, and toners.The colorant material can be produced by forming a solid resin using thepolymer compositions of the present invention, adding desired additivessuch as pigments, inks, dyes, or toners, and grinding the solid resinplus additive to a desired particle size. Molecular weights of colorantcarriers typically range from 5,000 to 1,500,000.

A further product type of the present invention includes powdermaterials. The powder materials can be produced by forming a solid resinusing the polymer compositions of the present invention and grinding thesolid resins to a desired particle size. Molecular weights of powdermaterials typically ranges from 2,000 to 1,000,000. Powder materials forcoatings should have good adhesive properties when melted to thesubstrate onto which it is affixed. The material should have goodflowability when melted in order to minimize pinholes in the coating.The chemical properties of the powder can vary based on the polymer andend use applications.

Additional information concerning suitable processes for preparingcompositions of the present invention can be found in copending U.S.applications Ser. No. 07/579,005 filed on September on Sep. 6, 1990 bySinclair and Ser. No. 07/579,465 by Sinclair filed on Sep. 6, 1990, thecontents of which are incorporated herein as if set forth in full.

MATERIAL PROPERTIES

The degradable polymer composition of the present invention has a widevariety of properties in addition to degradability which make thepolymer composition useful in numerous end use applications. Forexample, by varying the concentration of the components or processingconditions of the degradable polymer composition, the properties of thecomposition can be varied. For example, those properties includetoughness, flexibility, clarity, glossiness, adhesiveness,degradability, non-irritability, non-toxicity, water solubility, andheat shrinkability.

The materials of the present invention can be made more tough byincluding additives (i.e., modifiers or blended polymers) in the polymercomposition having a high modulus of elasticity or by adjusting theamount of cross-linking of the polymer, such that the impact resistanceof the polymer is increased to achieve desired levels.

The material of the present invention can also be made more flexible byincreasing the amount of modification of the polymer composition byeither internal or external modification which reduces the meltviscosity and/or lowers the glass transition temperature of the polymercomposition thereby increasing the flexibility of the polymercomposition to achieve standard desired levels.

Varying the amount of modification of the polymer compositions and theprocess conditions of the present invention also influences thediscoloration of the polymer composition. Referring to co-pending U.S.patent application Ser. No. 07/579,465, the application discloses apolystyrene substitute being a clear and colorless composition.Increasing the amount of modification increases the clarity of thepolymer composition by preventing heat build-up during processing of thepolymer composition which may cause discoloration.

Varying the amount of modification of the polymer compositions alsoaffects the glossiness of the polymer compositions. The glossiness ofthe polymer compositions is increased by altering the processing or thecomposition of the polymer compositions. For example, the polymercompositions may be processed using rough-surfaced molds or roughforming rolls to make the polymer less glossy.

The materials of the present invention can be made more adhesive byadjusting the amount of modification of the polymer composition. Byincreasing the amount of modification, the melting temperature of thepolymer composition is lowered and the melt viscosity is lowered,thereby increasing the adhesiveness of the polymer composition.

The degradability of the polymer compositions can also be controlledaccording to the methods discussed in detail above.

The materials can be non-irritable and non-toxic by appropriateselection of starting materials for the polymer and any externalmodifiers.

The polymer compositions can be made heat shrinkable by, for example,orienting films without subsequently heat setting them, as described indetail above.

The polymer compositions can be made more water soluble by increasingthe amount of water soluble co-monomers used in the polymer of thecomposition.

The polymer compositions used in materials of the present invention canalso include other components, such as hydroscopic additives, pigments,heat stabilizers, antioxidants, UV light absorbers, hydrophobicadditives, and insoluble additives. For example, hydroscopic additivescan be added to give the composition selectively permeable qualities tocompounds such as vapors, and to give the composition oil and surfactantresistance. Hydroscopic additives that can be added to the polymercomposition include, for example, cellulosic compounds such as starchesand wood flour. Pigments can be added to color the polymer compositionsif desired. Pigments can be effectively combined with polymercompositions by use of conventional pigment and pigment carriers.Suitable pigments can include, for example, iron oxide, lead oxide,strontium, chromate, carbon black, coal dust, titanium dioxide, talc,barium sulfate, cadmium yellow, cadmium red, and chromium yellow. Heatstabilizers can be added to the polymer compositions to enable thecompositions to be sterilizable without significant thermal degradationof the polymer compositions. Such heat stabilizers can include, forexample, zinc stearate, zinc lactate and sodium citrate. Anti-oxidantscan be added to prevent degradation of the compositions by free radicalsproduced by free radical generators such as ozone, gamma rays, and UVradiation. Anti-oxidants that can be added to the composition include,for example, pigments, sodium citrate, butylated hydroxy toluene,hydroquinones, and thiopropionates. UV light absorbers can be added tomake the composition more resistant to degradation by ultravioletradiation. Such UV radiation absorbers can include, for example, carbonblack, zinc oxide and substituted benzophenones. Hydrophobic additivescan be added to give the composition water resistance. Such hydrophobicadditives include, for example, silicone, oils and waxes. Insolubleadditives which migrate to the surface of the polymer composition can beadded prior to polymerization to give the composition a clingy quality,such as for film-like wrapping materials. Such insoluble additives caninclude, for example, calcium carbonate, mica and wood flour.

PRODUCT TYPES

The degradable material of the present invention is useful in numerousproduct types because while the material is degradable, it is typicallystable for a time sufficient to make it useful for a wide variety ofapplications.

The hydrolytically degradable material of the present invention isparticularly useful for the production of absorbent articles. Absorbentarticles can be produced by, for example, producing fibers out of thedegradable polymer composition of the present invention which can beadded to absorbent material to strengthen the material. Absorbentmaterials include materials able to absorb water, for example, materialable to absorb at least about 50 percent of weight of the article'sweight in water, more preferably at least about 500 percent of weight,and more preferably at least about 1,000 percent of weight. Sucharticles include, for example, towels, napkins, sponges, seed mats, seedstrips, tissues, and toilet paper. Towels can include paper towels andmultiple use towels similar to those sold under the trademark HANDIWIPES®¹.

Different material types of the hydrolytically degradable polymercomposition of the present invention are particularly useful for theproduction of products for the controlled release of chemicals.Controlled release products include products for sustained release ofchemicals and rapid release. Sustained release refers to the slowrelease of the chemicals contained in the product which differs fromrapid release of chemicals in, for example, a sudden burst. Chemicalsfor controlled release can include biocides, fertilizers, attractantssuch as chemicals used to attract pests into traps, repellents,pharmaceuticals, detergents, dyes, microbes, foods, water, and fabricsofteners. Chemicals can be microencapsulated or combined directly withthe claimed polymer compositions and released slowly upon degradation ofthe polymer compositions. The rate of release of such chemicals from thepolymer composition is dependent on the extent of degradability of thepolymer composition used to make the product, the concentration of theactive chemical on the product, and the method of association of thechemical with the product material.

Products for controlled release of chemicals can be produced from thebead-type material of the present invention including, for example,crowd control products including, for example, animal or peoplerepellent products. Animal repellent products can be used to control,for example, vermin. People repellent products can be used to control,for example, criminals and crowds. Crowd control products includeproducts such as tear gas release products. Other products forcontrolled release of chemicals include controlled release algaecides,controlled release mildewcides, controlled release of fungicides, waterirrigation biocides, detergent delivery systems, shoe polishes,encapsulated microbes, fertilizers including house plant food, animal orfish food, deodorized kitty litter, plant waterers, bug repellents, teargas, and water softeners. Products for controlled release of chemicalscan be produced from the fiber-type material of the present inventionincluding, for example, tree wrappings, and fabric softener deliverysystems. Products for controlled release of chemicals can be producedfrom the film-type material of the present invention including, forexample, preservative films, fragrance delivery systems, and foodtenderizer film. Products for controlled release of chemicals can beproduced from the injection molded-type material of the presentinvention including, for example, swimming pool conditioners, toiletbowl disinfectants, water line inserts, and chemical indicator stripsfor determining pH and color. Products for controlled release ofchemicals can be produced from the extruded profile-type material of thepresent invention including, for example, flea collars.

The hydrolytically degradable materials of the present invention can beinherently flammable. Thus, the materials can be particularly useful forthe production of flammable products including, for example, solid fuelsand warning flares. The materials can be used with ignition systems.

The hydrolytically degradable material of the present invention areparticularly useful for the production of oral drug delivery products,in particular capsules. The timing and rate of release of the drugcontained in the delivery product is dependent on the degradability ofthe polymer composition used to produce the delivery product. The rateof release is also dependent on the concentration and form of the drugcontained in the delivery product.

The adhesive-type hydrolytically degradable materials of the presentinvention are particularly useful for the production of adhesiveproducts such as, backing adhesives, hot melt adhesives, and pressuresensitive adhesives. The adhesiveness of a product is dependent on theviscosity of the polymer composition and the amount of polymercomposition used to produce the adhesive product. Such adhesives aretypically used on a variety of products, including labels, envelopes,adhesive tapes, boxboard adhesive, bumper stickers, lint removers, andtear away strips.

The hydrolytically degradable materials of the present invention can beinherently oleophilic, if thermoset and heat resistant. Thermosets aremade by including curable unsaturated polyesters in the presentcomposition. Thus, the materials can be particularly useful for theproduction of lubricants including, for example, petroleum-basedlubricants, graphite, fluorocarbons, silicones, natural waxes and oils,and lithium-based materials.

The hydrolytically degradable fiber material of the present invention isparticularly useful for the production of filter products.Representative examples of suitable uses includes filters such as coffeefilters and tea bags.

The hydrolytically degradable film-type material of the presentinvention is particularly useful for the production of a variety ofspecific bag-like products. Representative examples of suitable usesincludes products such as weather balloons, and bags for compost,fertilizer, seed, sand, basting, food produce, cereals, snack chips, petfood, sandwiches, trash, carry-out, single serve condiments, newspaper,and medical disposal. The film-type material is also useful forproducing multi-walled bags, liners for storage or shipping drums,Gaylord liners, plastic-lined paper bags for shipping and garbage,non-woven filter bags, sanitary napkin and air sickness bags, and meshbags. The toughness, flexibility, and degradability of the bags of thepresent invention will vary depending upon the requirements for specificproduct types. The toughness and flexibility of bags produced using thepolymer composition of the present invention is dependent on themodifier concentration of the polymer composition. The rate ofdegradation of the bags is dependent on the degradability of thecomposition.

Products such as containers can be produced from a variety of materialtypes of the hydrolytically degradable polymer composition of thepresent invention. Such material types have the characteristic of beingself-standing and include blow molded, coated paper, foam, injectionmolded, thermoformed and extruded profile types. The rigidity of theproduct is dependent on the molecular weight and concentration ofmodifier used to produce the polymer composition. Representativesuitable uses include food, including fast food, egg cartons, frozendinner, drink, dairy and produce containers, bottles, jugs, shipping orstorage drums, automotive and marine oil containers, containers used forcamping, photographic film containers, mailing tubes, caulk tubes,laundry powder containers, plastic envelopes, egg cartons, trays formeat, audio and visual cassettes, compact disk cassettes, jewelrycontainers, cigarette lighters, marine food service, tampon applicators,cosmetic containers, razor blade dispensers, shotgun shells, shotgunshell holders, oven pans, toner cartridges, paint can lids, and deli andfood storage containers.

The film-type material of the present invention is also useful aspackaging material such as, for example, butcher and deli paper, filmwrap, microwave cooking papers, gift wrap paper, bows and cards, ringsfor six packs of cans and bottles, cigarette packaging, floral wrap,motel and hotel glass wraps, blister packs, shrinkable wraps, bottle capsafety tamper evident wrap, plastic windows for viewing package contentssuch as windows for envelopes, print films for packaging, food productpackages and toiletry packages, vending machine packaging, and foam filldunnage. The protective quality of the packaging material is dependenton, for example, the toughness, flexibility, and heat shrinkability ofthe polymer composition used to produce the product.

The film, woven and non-woven material types of the hydrolyticallydegradable polymer composition of the present invention is useful in theproduction of clothing such as coats, pants, gloves, hats, shoes, boots,inner and outer layers of diapers, masks, pantyhose, and ponchos. Suchclothing are particularly suitable in situations where disposableclothing is needed such as in hospital use, sterile work, janitorialwork, work involving dangerous compounds such as radioactivity or toxicchemicals, and in research laboratories. The protective nature of theclothing product is dependent on the toughness of the polymercomposition used to produce the product.

The hydrolytically degradable polymer composition of the presentinvention is useful as an additive in the production of paper productsincluding, for example, junk mail, price tags, release liners foradhesive products, cardboard boxes, paper food containers, and signs.Addition of the polymer composition to conventional paper productsincreases the durability by increasing the wet strength of the paper.The degradability of the paper product is dependent on the amount anddegradability of the polymer composition added to the paper. Typicallysuch paper products can include between about 0.5 and about 10 weightpercent of polymer composition. The hydrolytically degradable propertyfacilitates recycling of mixed material products such as paper plasticlaminates. The laminates can be recycled by solubilizing thehydrolytically degradable polymer with an alkali wash and then recyclingthe solid paper fiber from the liquid monomer of the polymercomposition.

A variety of material types of the hydrolytically degradable polymercompositions of the present invention can be added to health products. Afilm-like material type can be used to produce health products such asbedding products for hospital applications, pet cage liners, deodorantpads, feminine hygiene napkins, seat covers, and bandages. A foam-likematerial type can be used to produce personal and home care productssuch as hair products, scrubbers, sponges, and mops. A fiber-likematerial type can be used to produce health products such as dentalfloss and toothbrushes. An injection-molded material type can be used toproduce health products such as tooth paste containers, mouthpieces forthermometers, syringes, micropipette tips, combs and hairbrushes,curlers, shavers, and waterpick tips. An extruded profile material typecan be used to produce health products such as supports for cottonswabs. An open pot molded material type can be used to produce healthproducts such as contact lenses.

A variety of material types of the hydrolytically degradable polymercompositions of the present invention can be used to produce healthproducts that need to be autoclaved prior to disposal. Contaminatedsolid health products produced using the polymer composition of thepresent invention can be heated at high temperatures to form sterileliquids for efficient disposal. Such health products include forexample, surgical and patient gowns, operating table and examinationtable sheets, intravenous tubing, catheter tubing, needles, syringes,bags for body fluids such as blood and plasma, and other disposablehospital supply goods.

A variety of material types of the hydrolytically degradable polymercompositions of the present invention can be used to produce substratessuitable for attachment and/or growth of living cells. Such substratescan be products for in vivo and/or in vitro growth of cells. As usedherein, the term "in vitro" refers to the growth of cells in anartificial environment. Without being bound by theory, it is believedthat living cells are able to attach and/or maintain cellular functions,such as growth and/or production of metabolites and proteins, due to:the morphology of the surface; the relative hydrophilic HLB; the ionicsurface characteristics of the polymer composition of the presentinvention. As such, substrates produced using the polymer composition ofthe present invention are useful, for example, for: growing skin cellsfor transplantation or in vitro testing of compounds frequentlyencountered by skin such as cosmetics and lotions; growing retinal cellsfor testing contact lens products; growing cells capable of producinguseful cellular products such as proteins, nucleic acids andcarbohydrates useful as pharmaceuticals and diagnostics; growinghematopoietic cells for transplantation; growing hair follicle cells fortransplantation; and growing chondroblasts and osteoblasts forreconstruction of cartilage and bone.

The polymer compositions of the present invention can be used to producematerial types selected from injection-molded products, fibers, extrudedand molded products, laminates, foams, powders and coatings, to producesubstrate products of variable dimensions suitable for culturing livingcells, including dishes, trays, sheets, flasks, slides, beads, tubes,filters and bottles.

Consumer products can be produced from a variety of material types ofthe hydrolytically degradable polymer composition of the presentinvention. A film-like material type can be used to produce homeproducts such as tablecloths, placemats, shower curtains, artificialChristmas trees, and Christmas tinsel. A fiber-like material type can beused to produce home products such as pipe cleaners. An injection moldedmaterial type can be used to produce home products such as toys forchildren and adults, paper clips, disposable camera bodies and lenses,and popsicle sticks. An extruded profile material type is used toproduce consumer products such as pens and pencils, shopping carts,fishing gear, camping gear, circuit breakers, twist-tie fasteners, pins,straws, toothpicks, and credit cards. A laminate material type can beused to produce consumer products such as mouse traps, roach traps, anddisposable dinnerware.

Garden products can be produced from a variety of material types of thehydrolytically degradable polymer composition of the present invention.A film-like material type can be used to produce a garden product suchas root ball cover, geo-textile erosion control, weed control film,mulch, seed mats, and seed strips. An injection molded material type canbe used to produce a garden product such as starter pots for plants,and, for example, seedling pots and substrates used in the culture ofplants by cloning. An extruded profile type can be used to producegarden products such as fencing stakes, garden marker stakes, and plantstakes.

The hydrolytically degradable polymer composition of the presentinvention is also particularly useful for producing automobile partssuch as tires and automobile interior parts. The ability to mold suchproducts is dependent on comonomer ratio, molecular weight of thepolymer product, and the choice and percentage of modifier added to thepolymer composition to produce the automobile part. In addition, thetackiness and adhesive strength required in automobile parts isdependent on the concentration of modifier in the polymer composition.

The hydrolytically degradable polymer composition of the presentinvention is also particularly useful for producing products forconstruction such as construction plastics and highway crack inducers.The film and extruded profile material types are particularly useful forthe production of such construction products. The toughness of theconstruction products is dependent on the concentration of modifieradded to the polymer composition used to produce the constructionproduct.

The hydrolytically degradable polymer composition of the presentinvention is also particularly useful for producing netting products.The fiber-type material of the present invention can be used to produceproducts such as netting, such as fish netting, erosion controllandscape netting and load consolidation netting. The strength of thenetting product is dependent on the amount of modifier added to thepolymer composition used to produce the netting.

The hydrolytically degradable polymer composition of the presentinvention is also particularly useful for producing rope products. Thefiber-type material of the present invention is added to produceproducts such as twine, bale banding, and ropes. The strength of therope product is dependent on the amount of modifier added to the polymercomposition used to produce the rope.

The hydrolytically degradable polymer composition of the presentinvention is also particularly useful for producing monofilament andmultifilament products. The fiber-type material of the present inventionis also useful for the production of the monofilament and multifilamentof paper towels.

The hydrolytically degradable polymer composition of the presentinvention is also particularly useful for producing polymer resins whichact as degradable replacements for products such as polyvinylchloride,polyethylene terepthalate, crystal polystyrene, impact-modifiedpolystyrene, low density polyethylene, linear low density polyethylene,and expandable polystyrene.

What is claimed:
 1. A paper product comprising paper fibers and apolymer composition comprising a hydrolytically degradable polymer and amodifier, wherein said modifier is compatible with said polymer and isnon-volatile and non-fugitive and wherein said polymer comprisesrepeating monomer or comonomer units selected from the group consistingof: ##STR17## wherein X is the same or different and is O or NR' with R'being the same or different and being H, hydrocarbyl, or substitutedhydrocarbyl; R₁, R₂, R₃ and R₄ can be the same or different and arehydrogen, hydrocarbyl containing 1 to 24 carbon atoms, or substitutedhydrocarbyl containing 1 to 24 carbon atoms, and where n₁ and n₂ can bethe same or different and are an integer of from 1-12; andwherein saidpaper fibers and said polymer composition are configured as a paperproduct.
 2. The paper product of claim 1, wherein said degradablepolymer comprises polylactic acid.
 3. The paper product of claim 1,wherein said degradable polymer comprises at least about 50 weightpercent repeating units derived from lactic acid or lactide.
 4. A paperproduct comprising paper fibers and a polymer composition comprising ahydrolytically degradable polymer, said polymer comprising:(a) abackbone chain; (b) first repeating units of the formula ##STR18##where, independently for each such first repeating unit: X₁ and X₂ areindependently O or NR' and R' is independently H, hydrocarbyl,substituted hydrocarbyl or a hydrocarbyl derivative; R₁, R₂ and Z₁combined have at most one carbon atom; R₃, R₄ and Z₂ combined have atmost one carbon atom; Z₁ and Z₂ are each independently one or moreconstituent group extending from the backbone chain and being covalentlybonded to an associated carbon atom in the backbone chain, at least oneof Z₁ and Z₂ being oxygen which forms a carbonyl group with theassociated carbon atom in the backbone chain; and the molecular weightof such a first repeating unit is less than about 145; and (c) fromabout 1 weight percent to about 50 weight percent, based on the totalweight of said polymer, of second repeating units of the formula##STR19## where, independently for each such second repeating unit: X₃and X₄ are independently O or NR' and R' is independently H,hydrocarbyl, substituted hydrocarbyl or a hydrocarbyl derivative; R₅,R₆, R₇ and R₈ combined have at least four carbon atoms; Z₃ and Z₄ areeach independently one or more constituent group extending from thebackbone chain and being covalently bonded to an associated carbon atomin the backbone chain, at least one of Z₃ and Z₄ being oxygen whichforms a carbonyl group with the associated carbon atom in the backbonechain; and wherein said paper fibers and said polymer composition areconfigured as a paper product.
 5. The paper product of claim 4, whereinsaid first repeating units are derived from lactic acid or lactide. 6.An absorbent article comprising an absorbent material having the abilityto absorb at least about 50 percent by weight of said material's weightin water and a polymer composition comprising a hydrolyticallydegradable polymer and a modifier wherein said modifier is compatiblewith said polymer and is non-volatile and non-fugitive and wherein saidpolymer comprises repeating monomer or comonomer units selected from thegroup consisting of: ##STR20## wherein X is the same or different and isO or NR' with R' being the same or different and being H, hydrocarbyl,or substituted hydrocarbyl; R₁, R₂, R₃ and R₄ can be the same ordifferent and are hydrogen, hydrocarbyl containing 1 to 24 carbon atoms,or substituted hydrocarbyl containing 1 to 24 carbon atoms, and where n₁and n₂ can be the same or different and are an integer of from 1-12;andwherein said absorbent material and said polymer composition areconfigured as an article selected from the group consisting of a towel,napkin, sponge, seed mat, seed strip, tissue and toilet paper.
 7. Theabsorbent article of claim 6, wherein said degradable polymer comprisespolylactic acid.
 8. The absorbent article of claim 6, wherein saiddegradable polymer comprises at least about 50 weight percent repeatingunits derived from lactic acid or lactide.
 9. An absorbent articlecomprising an absorbent material having the ability to absorb at leastabout 50 percent by weight of said material's weight in water and apolymer composition comprising a hydrolytically degradable polymer, saidpolymer comprising:(a) a backbone chain; (b) first repeating units ofthe formula ##STR21## where, independently for each such first repeatingunit: X₁ and X₂ are independently O or NR' and R' is independently H,hydrocarbyl, substituted hydrocarbyl or a hydrocarbyl derivative; R₁, R₂and Z₁ combined have at most one carbon atom; R₃, R₄ and Z₂ combinedhave at most one carbon atom; Z₁ and Z₂ are each independently one ormore constituent group extending from the backbone chain and beingcovalently bonded to an associated carbon atom in the backbone chain, atleast one of Z₁ and Z₂ being oxygen which forms a carbonyl group withthe associated carbon atom in the backbone chain; and the molecularweight of such a first repeating unit is less than about 145; and (c)from about 1 weight percent to about 50 weight percent, based on thetotal weight of said polymer, of second repeating units of the formula##STR22## where, independently for each such second repeating unit: X₃and X₄ are independently O or NR' and R' is independently H,hydrocarbyl, substituted hydrocarbyl or a hydrocarbyl derivative; R₅,R₆, R₇ and R₈ combined have at least four carbon atoms; Z₃ and Z₄ areeach independently one or more constituent group extending from thebackbone chain and being covalently bonded to an associated carbon atomin the backbone chain, at least one of Z₃ and Z₄ being oxygen whichforms a carbonyl group with the associated carbon atom in the backbonechain; andwherein said absorbent material and said polymer compositionare configured as an absorbent article.
 10. The absorbent article ofclaim 9, wherein said first repeating units are derived from lactic acidor lactide.